Physics(forces)
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- Created by: JemimaStubbs
- Created on: 07-04-21 15:44
what is a scalar? give examples
only have a magnitude eg. speed, energy,
time and distance
time and distance
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what is a vector? give examples
have a magnitude and direction eg. force,
velocity, displacement, momentum and
acceleration
velocity, displacement, momentum and
acceleration
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Distance vs displacement?
Distance is the total distance covered and
displacement is distance traveled in
certain direction
displacement is distance traveled in
certain direction
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Speed vs velocity?
Speed of an object does not depend on the
direction in which it is traveling but the velocity
of an object depends on the speed and direction
in which it is moving
direction in which it is traveling but the velocity
of an object depends on the speed and direction
in which it is moving
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what does the gradient of a distance-time
graph mean?
graph mean?
the gradient (slope) of a distance-time graph
tells us the speed, the higher the speed the
steeper the gradient, if an object is stationary
the gradient is zero
tells us the speed, the higher the speed the
steeper the gradient, if an object is stationary
the gradient is zero
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what is speed? and how do you find the
average speed?
average speed?
speed is the distance moved by an object in 1
second. it is measured in m/s
average speed (m/s) = distance traveled (m)
time taken (s)
second. it is measured in m/s
average speed (m/s) = distance traveled (m)
time taken (s)
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typical speed for; walking?
running? cycling?
running? cycling?
walking=1.5m/s
running=3m/s
cycling=6m/s
running=3m/s
cycling=6m/s
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what does the gradient of a velocity-time graph
mean?
mean?
the gradient of a velocity-time graph tells us
the acceleration, the greater the acceleration
the steeper the gradient, if the gradient is zero
the object is moving at a steady velocity
the acceleration, the greater the acceleration
the steeper the gradient, if the gradient is zero
the object is moving at a steady velocity
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how do you calculate acceleration from a
velocity-time graph?
velocity-time graph?
acceleration(m/s2)=velocity(m/s)
time(s)
time(s)
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what does the area under a velocity-time
graph mean?
graph mean?
the area under is the distance traveled
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how do you find acceleration from a velocity-time
graph when the graph is a curve?
graph when the graph is a curve?
draw a tangent at the point on the graph, find the
gradient of the tangent
gradient of the tangent
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how do you find the total distance traveled using
a velocity-time graph that is a curved graph?
a velocity-time graph that is a curved graph?
If more than half the square is under the graph,
count it as a whole square, if less than half
the square is under the graph, don't count the square
count it as a whole square, if less than half
the square is under the graph, don't count the square
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when an object changes its velocity what is it
doing?
doing?
the object is accelerating
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what are the three ways that an object can be
accelerating?
accelerating?
*if it is speeding up
*if it is changing direction
*if it is slowing down, negative deceleration
*if it is changing direction
*if it is slowing down, negative deceleration
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what is the acceleration equation?
acceleration=change in velocity
time taken
a=v-u
t
u=v-at
v=at+u
t=v-u
a
time taken
a=v-u
t
u=v-at
v=at+u
t=v-u
a
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how do you find acceleration when you know the distance and the change in velocity?
v2-u2=2as
a=v2-u2
2s
acceleration=final velocity2-initial velocity2
2xdistance
a=v2-u2
2s
acceleration=final velocity2-initial velocity2
2xdistance
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how do you calculate stopping distance?
thinking distance + braking distance
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what is thinking distance?
this depends on the drivers reaction time. if the
driver if fully alert then a typical adult will take
0.7s to react to a hazard and start breaking,
thinking time. distance traveled is thinking distance and if the car is traveling at a faster speed then
driver if fully alert then a typical adult will take
0.7s to react to a hazard and start breaking,
thinking time. distance traveled is thinking distance and if the car is traveling at a faster speed then
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factors that may increase the drivers reaction
time?
time?
*phone
*loud music
*alcohol/drugs
*tiredness
*loud music
*alcohol/drugs
*tiredness
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what is breaking distance?
the distance covered once the driver has pressed
the break pedal and the car is converting kinetic
energy into thermal energy by friction. the drag
of air resistance also helps slow the car
down
the break pedal and the car is converting kinetic
energy into thermal energy by friction. the drag
of air resistance also helps slow the car
down
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what factors may increase breaking distance?
*velocity
*mass
*road conditions (rain)
*car conditions (breaks,tires)
*mass
*road conditions (rain)
*car conditions (breaks,tires)
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what happens when a driver breaks?
the brakes grip the wheels to slow the wheels, as the wheels slow down friction between the
tyres and the road increase to slow the car.
tyres and the road increase to slow the car.
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what is skidding?
if the driver breaks too hard the wheels lock
and the car skids. the friction from the road
cannot slow the car as fast as the breaks are
slowing the wheels.
and the car skids. the friction from the road
cannot slow the car as fast as the breaks are
slowing the wheels.
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what is a contact force? how does it work?
a force exerted on each object lasts for as long
as the objects are in contact, once they are
apart, the forces no longer exist and the
interaction has ended, the forces arise during
the interaction, a force cannot be 'put into' or
'stored in' an obj
as the objects are in contact, once they are
apart, the forces no longer exist and the
interaction has ended, the forces arise during
the interaction, a force cannot be 'put into' or
'stored in' an obj
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examples of contact forces?
-normal contact force(ground supporting your weight eg. chair on floor)
-friction(eg. tyres on a road)
-drag(air/water resistance)
-upthrust(buoyant eg. submarine)
-tension(extension eg swing)
-friction(eg. tyres on a road)
-drag(air/water resistance)
-upthrust(buoyant eg. submarine)
-tension(extension eg swing)
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examples of non-contact forces?
-electric force
-gravitational force(eg. roller coaster, HEP)
-magnetic force(eg. phones, fridge magnet)
-gravitational force(eg. roller coaster, HEP)
-magnetic force(eg. phones, fridge magnet)
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what are forces measured in?
forces measured in newtons
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when two objects apply forces to each other we
say they .....
when two objects ...... there are always two forces
they are the .... in size and ..... in direction
which of newtons laws is this?
say they .....
when two objects ...... there are always two forces
they are the .... in size and ..... in direction
which of newtons laws is this?
when two objects apply forces to each other we
say they INTERACT when two objects INTERACT there are always two forces they are the SAME in size and OPPOSITE in direction
this is newtons third law
say they INTERACT when two objects INTERACT there are always two forces they are the SAME in size and OPPOSITE in direction
this is newtons third law
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which of newtons laws states what is happening when the forces acting on an object are equal? and what does it say will happen?
newtons 1st law says that if the resultant force is zero than the object will be either stationary or moving at a constant speed.
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what happens if the forces acting on an object are unbalaced?
if the forces are unbalanced, the object will be accelerating, it will be changing in either direction or speed.
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what is the equation for weight using mass and gravity?
weight(N)=mass(g)xgravitational field strength(N/kg)
w = m x g
w = m x g
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what is mass?
what is weight?
what is weight?
mass is the amount of matter, measured in kg
weight is the pull of gravity on an object, measured in N, depends on how much matter an object has and the gravitational field strength
weight is the pull of gravity on an object, measured in N, depends on how much matter an object has and the gravitational field strength
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what is earths gravitational field strength?
each kilogram of mass has a weight of 10N, earths gravitational field strength is 10N/kg (9.81)
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what is the gravitational field strength on....
moon?
mars?
Jupiter?
deep space?
moon?
mars?
Jupiter?
deep space?
moon=1.7
mars=4
Jupiter=25
deep space=0
(all in N/Kg)
mars=4
Jupiter=25
deep space=0
(all in N/Kg)
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what is the resultant force?
the sum of all the forces acting - taking direction into consideration
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finding a resultant force by adding sides to make
a parallelogram?
a parallelogram?
add two lines parallel to the twp already drawn,
draw a line from where the two lines meet
to the opposite diagonal corner, us the scale to convert the length into the magnitude .
draw a line from where the two lines meet
to the opposite diagonal corner, us the scale to convert the length into the magnitude .
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what is resolving forces?
drawing rectangle forces to show the vertical and
horizontal components
horizontal components
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what is the relationship between the incline
and the force needed to get up the incline?
and the force needed to get up the incline?
as the angle increases, the incline increases and
the force needed is greater
the force needed is greater
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the larger the mass the ... the acceleration for a
given force
the larger the force the ... the acceleration for a
given mass
given force
the larger the force the ... the acceleration for a
given mass
the larger the mass the SMALLER the
acceleration for a given force
the larger the force the LARGER the
acceleration for a given mass
acceleration for a given force
the larger the force the LARGER the
acceleration for a given mass
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What is the equation that links force and
acceleration?
acceleration?
resultant force (N) = mass (kg) x acceleration (m/s2)
F=mxa
F=mxa
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what is Newtons 1st law?
When the resultant force acting on an object is zero then;
*the object remains stationary
*the object continues to move at the same speed and the same direction, therefore the same
velocity
*the object remains stationary
*the object continues to move at the same speed and the same direction, therefore the same
velocity
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what is Newtons 2nd law?
the acceleration of an object is proportional to the resultant force acting on the object, and inversely proportional to the mass of an object
force=mass x acceleration
f=mxa
force=mass x acceleration
f=mxa
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what is Newtons 3rd law?
Whenever two objects interact, the force that body A exerts on body B, is equal and opposite to the force that body B exerts on body A
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when an object moves through a fluid eg. air or water, the fluid drags on the object. Air and water resistance always act to oppose the motion of the object. there friction forces are often called ....
drag forces
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what does the size of the drag force
depend on?
depend on?
~the shape of the object[fast moving objects are made more streamlined to reduce drag]
~the type of fluid the object is moving through[water exerts more drag tan air]
~the speed of the object[drag forces increases with speed]
~the type of fluid the object is moving through[water exerts more drag tan air]
~the speed of the object[drag forces increases with speed]
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what is terminal velocity?
(muffin case example)
(muffin case example)
when the case is first dropped, the only force acting on it is weight which causes the case to accelerate due to newtons 2nd law as there is a constant velocity. as the case falls the air exerts a force on the case, air resistance, the velocity increases
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terminal velocity cont.
eventually the forces of weight and air resistance are equal and the resultant force is zero so the case falls at a constant velocity due to newtons
1st law. this is the terminal velocity.
1st law. this is the terminal velocity.
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what do the symbols;
a?
u?
v?
s?
t?
a?
u?
v?
s?
t?
a=acceleration
u=initial velocity
v=final velocity
s=distance
t=time
u=initial velocity
v=final velocity
s=distance
t=time
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Elastic deformation; if a material deforms elastically then …
The extension is directly proportional to the force on it
It returns to original length when the force is removed
It returns to original length when the force is removed
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Inelastic deformation; if a material deforms inelastically then …
It will have a curved force-extension graph
It may not return to its original length when the force is removed
It may not return to its original length when the force is removed
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What is Hooke’s law?
The extension of an elastic object is directly proportional to the force applied providing we do not exceed the limit of proportionality
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Do rubber bands obey Hooke’s law?
Rubber is a very stretchy material made of long molecules which are tangled up in the unstretched band. When a force is applied to the band the molecules untangle to give large extensions. Once the molecules on tangled the band becomes much harder to stre
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Do plastic bands obey Hooke’s law?
The polythene ***** is quite stiff. The extensions up to 4 N are quite small. After 4 N the polythene bag ‘gives’ on stretches easily.
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What is the equation for elastic materials obeying Hooke’s law?
F=k e
F= the force or load of material in Newton’s
e= the extension of the material in metres
k= the spring constant in Newtons/metre
F= the force or load of material in Newton’s
e= the extension of the material in metres
k= the spring constant in Newtons/metre
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What is a spring constant? And what does a large spring constant mean?
The spring constant, k, of a spring is the force per unit extension (per m) needed to stretch it (assuming it hasn’t passed its limit of proportionality)
A larger k -> stiffer spring -> larger force to stretch it
A larger k -> stiffer spring -> larger force to stretch it
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What is elastic potential energy?
When a spring is stretched, the work done is stored as elastic potential energy. Providing the spring is not elastically deformed the work done on the spring and the elastic potential energy stored are equal.
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What is the equation for elastic potential energy stored?
Elastic potential energy (in J) = 0.5 x spring constant (in N/m) x (extension)2 (in m)
Ee=1/2 k e2
Ee=1/2 k e2
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What is work done?
Work is done only one object is moved by a force. The larger the force and the greater the distance moved by the object then the more work is done. Work done is measured in joules J : 1J is work done when a force of 1N moves 1m. When work is done energy i
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What is the equation for work done?
Work done= force x distance moved in the direction of the force
W = F x s
W = F x s
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How do you calculate energy transferred?
Energy transferred (in J) = Work done (in J) =
force (in N) x distance moved in the direction of
the force (in m)
force (in N) x distance moved in the direction of
the force (in m)
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What is power?
Power is the rate at which work is done or the rate at which energy is transferred. The greater the amount of energy transferred on the shorter the time it takes for the energy to be transferred, the greater the power. Power is measured in watts ‘W’. One
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What is the equation for power?
Power = work done. Or P= W
Time taken. t
Power = energy transferred P= E
Time taken. t
Time taken. t
Power = energy transferred P= E
Time taken. t
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What contains gravitational potential energy?
An object which is lifted up against gravity gains gravitational potential energy
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How do you calculate the change in gravitational energy?
Change in gravitational energy= weight x change in height Ep = m x g x h
(Change in gravitational energy = mass x g x change in height, as weight = mass x gravitational field strength W=m x g
(Change in gravitational energy = mass x g x change in height, as weight = mass x gravitational field strength W=m x g
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What is kinetic energy and what does it depend on?
Kinetic energy is the energy of a moving object. It depends on two things: the mass, m of the object (in kg) and The velocity, v (or speed) of the object in metres/second
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How do you calculate the kinetic energy of an object in joules?
Ek = 1/2 x m x v2
Kinetic energy = 1/2 x mass x velocity (squared)
Kinetic energy = 1/2 x mass x velocity (squared)
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What is the link between gravitational potential energy and kinetic energy?
There is an interchange, always equal the same amount when added, example ( diver has 600J of potential energy on diving board and 0J of kinetic energy, when he reaches the water he has 600J of kinetic energy and 0J of potential energy, so at any point Ep
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Wha is the centre of mass of an object?
The centre of mass of an object is the point where all of the mass of the object appears to be concentrated
The weight of the object, W, (pull of gravity) appears to act down from the centre of mass
The weight of the object, W, (pull of gravity) appears to act down from the centre of mass
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Do you find the centre of mass of an object by balancing?
When an object is supported with a pivot directly below its centre of mass, the weight of the object will act through the pivot: the object will remain in equilibrium
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Do you find the centre of mass of an object if the object is uniform in thickness and symmetrical in shape?
If the object is uniform the centre of mass will be at the exact geometric centre. For the uniform shapes, the centre of mass is a long each of the axis of symmetry. The centre oficial it is where are the axis of symmetry meet
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Do you find the centre of mass of an object if the object is uniform in thickness but not symmetrical in shape?
If an object is freely suspended It will come to rest with its centre of mass directly below the point of suspension. This is because the weight exerts no turning affect on the object when it is directly below the suspension point.
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How do you find the centre of mass of an irregular lamina?
The apparatus is arranged (lamina is pinned So it is suspended and can move a plumline is suspended in front of the lamina) The lamina is allowed to swing freely and come to rest and the centre of mass must be directly below the pin. The plumbline is used
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What is the rule for toppling and stability?
An object is stable providing a line of action of its weight acts within the base of the object. If the line of action of the weight of an object lies outside the base, there will be a resultant moment and the object will topple.
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How do you increase stability?
The position of the centre of gravity; The lower the centre of gravity is the most stable the object, the higher It is more likely the object is to topple over if it is pushed. Increase in the area of the base; This will increase The stability of an objec
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What is a moment?
The moment of a force is the turning effect that it has about a pivot, measured in Newton metres (Nm)
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What are the two factors that the ability of a force turn on object depends on?
The size of the force that acts At right angles to the line through the pivot point
The perpendicular distance the force is applied from the pivot point
The perpendicular distance the force is applied from the pivot point
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How do you calculate the mount of a force?
Moment = force x perpendicular distance from the line of action of the force to the pivot
M (in Nm) = F (in N) x d (in m)
M (in Nm) = F (in N) x d (in m)
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How do you increase the moment?
1. Increase the size of the force
2. Increase the perpendicular distance of the line of action of the force from the pivot
2. Increase the perpendicular distance of the line of action of the force from the pivot
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What is the principal of moments?
For an Object in equilibrium (balance) the sum of the clockwise moments about the point is equal to the sum of anticlockwise moments about that point.
Clockwise moments = anti-clockwise moments
Clockwise moments = anti-clockwise moments
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What are gears?
He is consist of toothed wheels Fixed to shafts. The teeth interlock, and as the first shaft (driver shaft) rotates, the motion is transmitted to the second or driven shaft
(Gears turn in opposite directions)
(Gears turn in opposite directions)
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What is the Relationship between forces and moments on different size gears?
The force acting on the teeth are identical for both gears, but the moments are different for different size gears
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What happens when you change the size of the driven gear?
If a driven gear gets bigger, It rotates more slowly but with a greater moment e.g. low gear on a bike
If a driven gear gets smaller, It rotates more quickly but with a small the moment e.g. high gear on a bike
If a driven gear gets smaller, It rotates more quickly but with a small the moment e.g. high gear on a bike
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What are the main reasons we use gears?
To increase speed (as if the driver has more teeth than the driven the second one has to turn faster to keep up this means the second wheel turns faster than the first one but with less force this is a distance multiplier). To increase force (If the drive
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What is the equation that relate the teeth on the gear on the speed of the gear? And what would happen if the system was 100% efficient?
No. Of teeth on driven gear = speed of driven gear
No. Of teeth on driver Speed of driver gear
If the system is 100% efficient then if the speed of rotation doubles the force produced at the driven gear will be half
No. Of teeth on driver Speed of driver gear
If the system is 100% efficient then if the speed of rotation doubles the force produced at the driven gear will be half
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What is momentum?
All moving objects have momentum
It is a measure of how difficult it is to stop a moving object
It is a measure of how difficult it is to stop a moving object
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How do we increase momentum?
The greater the mass of an object and the faster it is moving the greater the momentum is.
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How to calculate momentum?
Momentum = mass x velocity
P= m x v
(In kg m/s) = (in kg) x (in m/s)
P= m x v
(In kg m/s) = (in kg) x (in m/s)
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What is the principle of conservation of momentum?
In all collisions/interactions (providing no external forces act) Momentum is conserved. This means that momentum before the collision = Momentum after the collision
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Why is momentum conserved in collisions?
When two objects collide the force is that they exert on each other * are the same size * act for the same time * are in opposite directions
This means that the change in momentum of each object is the same amount but in opposite directions, So one object
This means that the change in momentum of each object is the same amount but in opposite directions, So one object
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Using a canon as an example, explain how momentum is conserved when it starts as 0
Before the explosion, the Cannon and Ball are both stationary so the total the momentum is zero. After the explosion the momentum of the ball moving to the right is equal but opposite to the momentum of the camera moving to the left so the total momentum
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How can you change the momentum of an object?
You can change the momentum of an object by exerting a force on it for a time. You can give a stationary object some momentum by exerting a force on it to make it move. To increase the momentum of a moving object you must exert a force which act in the sa
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How do you produce a bigger change in momentum?
1. Use a bigger force
2. Apply the force for a longer time
2. Apply the force for a longer time
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How do you calculate the change in momentum?
Change in momentum (in kg m/s) = force (in N) x time (in s)
(Triangle)p= F x t
(Triangle)p= F x t
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Explain how a seatbelt helps to reduce injuries in the event of car crash?
>seatbelt stretches as the car comes to a stop
>this increases the time taken for the person to come to rest
>this increases the time taken for the momentum to change
>which decreases the impact force on the passenger
>this increases the time taken for the person to come to rest
>this increases the time taken for the momentum to change
>which decreases the impact force on the passenger
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Other cards in this set
Card 2
Front
what is a vector? give examples
Back
have a magnitude and direction eg. force,
velocity, displacement, momentum and
acceleration
velocity, displacement, momentum and
acceleration
Card 3
Front
Distance vs displacement?
Back
Card 4
Front
Speed vs velocity?
Back
Card 5
Front
what does the gradient of a distance-time
graph mean?
graph mean?
Back
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