# Physics

• Created by: Normska
• Created on: 10-11-17 12:25
F = m x a ?
Force (N) = mass (kg) x acceleration (m/s2). The relationship between unbalanced force and, mass and acceleration
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W = m x g ?
Weight (N)= mass (kg) x gravitational field strength (N)
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p = m x v ?
momentum = mass (kg) x velocity (m/s)
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What is the relationship between force, change in momentum and time taken?
force = change in momentum / time taken
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What is a Scalar?
physical quanties that are described by magnitude only. e.g. time, volume, speed, temperature
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What is a Vector?
physical quanities that are described by magnitude (size) and direction. e.g. Force, velocity, acceleration, force, mass, momentum, energy, work, power, etc.
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What is Resultant Force (F res) ?
A single force which has the effect on the body as the original forces all acting together. The Vector sum of all the forces.
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Draw a diagram showing Resultant Force
Box with 3 arrows (f1, f2, f3) pushing it. Then on the other side of th box 1 arrow (f4)
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How is a vector shown on a diagram?
An arrow drawn to scale. Tail -------> Head
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What is Newton's 1st law ?
Every object continues in its state of rest or uniform motion in a straight line, unless it is compelled to change taht state by and external force acting on it. (Law of Inertia!))
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What is inertia?
Inertia is that property of a body that resists a change in motion
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Give an example of inertia
1) The passenger in a running bus tends to lean forward , when the bus stops suddenly:When the bus is running, the whole body of the passenger is in the state of motion. When the bus stops suddenly, the lower part of the passengers body whih is in 
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Give an example of Newton's 1st law
A car will maintain a constant speed if hte drive force and the drag are balanced. i.e. The total (resultant) force is zero
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What is a balanced force ?
A balanced force is when the forces are balanced i.e. they are of equal size, but opposite in direction. 10N 10N. Note this does not mean there is no force.
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Give an example of balanced forces on a stationary object
1) If an object is stationary, it will continue to be stationary. If you are sitting on a chair, your weight is balanced by an upwards force from the chair.
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Give an exampe of a balanced force on a moving object
If an object is moving, it will move at a constant speed. If you are pedalling a bicycle at a constant speed, the force you put into the pedals is balanced by the air resistance and friction.
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Explain why a car has a maximum speed
The engine has only a limited force it can provide. Eventually the air resistance (and friction) balance out the force the engine can provide and so the car cannot go any faster.
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What is Newton's 2nd Law ?
If an unbalanced or resultant force acts on an object then the object will accelerate in the direction of the resultant force, the acceleration will be directly proportional to the resultant force and inversely proportional to the mass of the object
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F res = ma ?
Resultant Force (N) = mass (kg) x acceleration (m/s2)
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What is Force measured in?
N - Newtons
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What is Mass measured in?
Kg - Kilogrammes
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What is Acceleration measured in ?
m/s 2 - metres per second (squared) or metres per second per second
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What is Acceleration always caused by?
Acceleration is always caused by Resultant Force
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Is a Resultant Force balanced, unbalanced or can it be either?
Resultant Force will be balanced if the forces are from opposite directions and are equal, or unbalanced if one force is greater than the others. but Unbalanced Force
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Which direction is Acceleration (in relation to Resultant Force)
Acceleration is always, without exception, in the same direction as the resultant force.
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What is an Unbalanced Force?
Forces that cause a change in the motion of an object are unbalanced forces
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Give an example of an Unbalanced Force on a stationary object
With an unbalanced force an object will accelerate i.e it will move from being stationary
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Give an example of a Balanced Force on a moving object
If the object is moving at a constant speed, it will accelerate to a higher speed
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What is Newton's 3rd Law ?
If a body A exerts a force on body B, body B must exert an equal and opposite force on body A. For every action there is an equal and opposite reaction.
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Give an example of Newton's 3rd Law on a stationery object
A book resting on a table. The book is pulled down by the Earth’s gravity, and this force is balanced by the reaction force from the table top.
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Give an example of Newton's 3rd Law on a moving object
a car crashing into a tree. The car and tree exert equal and opposite forces on each other in the collision.
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Give an example of forces acting in pairs (Newton III pairs)
Book on table vs table on book, book on earth vs earth on book
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Draw a free body diagram of a book on a table
Book on table (weight), table on book (reaction force)
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a = F res/ m ?
Acceleration (m/s2) = Resultant force (N) / Mass (kg)
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What is a net force also known as?
A net force is also known as a resultant force
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Can you explain the practical on "The relationship between Force and Acceleration" ?
Please learn. Learn the graph too.
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Do you understand how to calculate Balanced and Unbalanced Forces?
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Can you explain the practical on "Finding the acceleration of falling objects?"
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Give an example of terminal velocity?
Objects falling through a fluid eventually reach terminal velocity, when the resultant force acting on them is zero and they are moving at a steady speed. Weight is a force exerted on an object because of a gravitational force.
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What is terminal velocity?
When the friction (upwards force) equals the weight (downward force). There is no acceleration therefore the velocity is constant
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In vehicle stopping distances what factor affects the 'thinking distance'?
The driver
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In vehicle stopping distances what factors affects the 'breaking distance'?
The tyres, the breaks or the road
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What effect does a wet road have on stopping distance?
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What effect does a tired driver have on stopping distance?
Slower reaction time
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What effect does a higher velocity before braking have on stopping distance?
The car will travel a longer distance per second.
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Draw a velocity - time graph showing a car slowing from 20 m/s to rest in 2 seconds
Velocity (20 m/s) on y axis, Time ( 2 secs) on x axis. Draw straight line
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Draw a velocity-time graph showing a car travelling at 30mph, thinking distance 9m and braking distance 14m.
see notes
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Draw a velocity-time graph showing a card travelling at 20m/s, thinking distance 0.5 seconds, deceleration at 2 m/s2
see notes
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What is weight measured in?
N - Newtons
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How do you label a graph?
Y (up to the sky) name and units. X (name and units). Regular intervals. Title. (Key or legend if needed)
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## Other cards in this set

### Card 2

#### Front

Weight (N)= mass (kg) x gravitational field strength (N)

W = m x g ?

### Card 3

#### Front

momentum = mass (kg) x velocity (m/s)

### Card 4

#### Front

force = change in momentum / time taken

### Card 5

#### Front

physical quanties that are described by magnitude only. e.g. time, volume, speed, temperature

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