Motion and Forces

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What is the difference between the speed of an object and its velocity?
speed is a scalar quantity and velocity is a vector quantity
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What is acceleration?
A measure of how quickly the velocity of something is changing, it can be positive if the object is speeding up or negative its slowing down
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Is acceleration a vector or a scalar?
Vector
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Are forces vector or scalar?
Vector
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What is the resultant force?
The total force that results from two or more forces acting on a single object
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How do you work out the resultant force?
If the forces are acting in the same direction, add them together
If there acting in opposite directions subtract one from the other
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If the resultant forces on an object are 0, we say they are ........?
balanced
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If there is a non-zero force on an object, the forces are .........?
unbalanced
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What is Newtons first law?
A moving object will continue to move at the same speed and direction unless an external force acts on it
A stationary object will remain at rest unless an external force acts on it
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Will balanced forces (zero resultant force) change the velocity of an object?
no
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How will unbalanced forces (non-zero resultant force)
They'll change the speed and/or direction of an object.
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An object moving in a circle has changing ...... even though its ..... remains the same.
Velocity
Speed
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What is a centripetal force?
A force that causes objects to follow a circular path. The force acts towards the centre of the circle.
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What is mass?
The quantity of matter there is inside an object, and only changes if the object itself changes.
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What is weight?
A measure of the pull of gravity on an object and depends on the strength of gravity.
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What is gravitational field strength?
What's its unit?
A measure of how strong the force of gravity is somewhere. The units are newtons per kilogram (N/Kg)
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What's the gravitational field strength of earth?
About 10 N/Kg
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What's the calculation for weight?
Weight (N) = Mass (Kg) x gravitational field strength (N/Kg)
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On earth falling objects have a force of what as well as weight?
air resistance
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What does Newton's second law state?
The acceleration in the direction of the resultant force depends on:
the size of the force (for the same mass the bigger the force the bigger the acceleration.
the mass of an object (for the same force, the more massive the object the smaller the acceler
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What's the calculation for force?
Force (N) = Mass (Kg) x Acceleration (m/s²)
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Define inertial mass.
The mass of an object found from the ratio of force divided by acceleration. The value is the same the mass calculated from the weight of an object and gravitational field strength.
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What is inertia?
the tendency for an object to keep moving with the same velocity.
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What does the inertial mass of an object do?
Measures how difficult it is to change the velocity of an object.
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What is Newtons third law about?
The force on two different objects when they interact with each other,
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When can this interaction happen?
When objects touch, such as when you sit on a chair.
At a distance, such as the gravitational attraction between the earth and the moon.
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Define action- reaction forces.
Pairs of forces on interacting objects. There always the same size, in opposite direction and acting on different objects.
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How are action-reaction forces different to balanced forces?
Balanced forces act on the same object, action-reaction forces act on different objects.
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Define equilibrium.
When a situation is not changing because all things affecting it balance out.
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The action and reaction forces that occur during a collision are the same ......, but do not necessarily have the same effect on the two objects because the objects have ...... .......?
Size
Different
Masses
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What is momentum?
A measure of a tendency of an object to keep moving - or how hard it is to stop it moving
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Is momentum vector or scalar?
Vector
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What is the calculation for momentum?
Momentum (kg m/s) = Mass (Kg) x Velocity (m/s)
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What's the equation for force using momentum?
Force = change in momentum ÷ time
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When moving objects collide, what is the total momentum of both objects?
It's the same before the collision and after the collision as long as there are no external forces acting on it.
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Define conservation of momentum.
The total momentum of moving objects before a collision is the same as the total momentum afterwards as long as no external forces are acting.
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Define thinking distance.
The distance travelled by a vehicle while the driver reacts.
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Define braking distance.
The distance travelled by a vehicle while the brakes are working to bring to a halt.
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Define stopping distance.
The distance in which a car stops, which is the sum of the thinking and braking distance.
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Define reaction time.
The time taken to respond to a stimulus, which is affected by the speed of activity in the brain and the nervous system.
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Define stimulus.
(Plural: stimuli) A change in a factor (inside or outside the body) that is detected by receptors such as sight or sound.
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Define response.
An action that occurs due to a stimulus.
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What's the sum for stopping distance?
Thinking distance + Braking distance
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How can response times be measured?
Computors or electric circuits that measure the time between a stimulus and a response.
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What's the typical reaction time to a stimulus?
0.25 seconds
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What can make this time longer?
If a person is ill, tired or has been taking drugs or drinking alcohol.
Or distractions such as using a mobile phone.
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What do car brakes use to slow the car down?
friction
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if the brakes are worn, they create ...... ...... and do not slow the vehicle as effectively.
Less friction
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What can increase the braking distance?
If the road is wet or has loose gravel on it, or if the tyres are worn.
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if a vehicle has more mass, more ...... is needed to decelerate it?
Force
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If they same amount of friction is used to stop a vehicle, a ...... vehicle will travel further than a ....... vehicle .
Heavier
Lighter
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The force used to accelerate an object transfers energy, the amount of energy transferred depends on what?
The size of the force and how far the object moves while the force is pushing it.
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What's the calculation for work done?
Work done (J) = Force (N) x Distance moved in the direction of the force (m)
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Define work done
A measure of the energy transferred when a force acts through a distance.
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What is the energy stored in moving objects called?
Kinetic energy.
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The amount of kinetic energy depends on what?
The mass of an object and its velocity.
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What's the calculation for kinetic energy?
Kinetic energy (J) = ½ x Mass (Kg) x (speed)² (m/s)²
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When a vehicle stops, what happens to the kinetic energy?
It's transferred to other energy stores by the braking force.
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Slowing down is a ......?
Deceleration
(Negative acceleration)
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The force needed for any kind of acceleration depends on what?
The size of the acceleration and the mass of the object.
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Why do modern cars have lots of safety built in?
To help reduce the force on the occupants in a collision.
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Define a crumple zone.
A vehicle safety device in which part of the vehicle is designed to crumple in a crash, reducing the force of the impact.
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How do crumple zones work?
If the car hits something it takes a little time for this crumpling to happen, so the declaration of the car is less and the force on the car is also less than if it had a more solid front.
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What do seatbelts and airbags do?
Seat belts hold the passengers into the car and airbags increase the time it takes for a person's head to stop in a collision.
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What does the force in a road collision depend on?
The change of momentum as the car comes to a stop.
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How do we calculate this force?
Force = (momentum x final velocity - momentum x initial velocity) ÷ time
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Other cards in this set

Card 2

Front

What is acceleration?

Back

A measure of how quickly the velocity of something is changing, it can be positive if the object is speeding up or negative its slowing down

Card 3

Front

Is acceleration a vector or a scalar?

Back

Preview of the front of card 3

Card 4

Front

Are forces vector or scalar?

Back

Preview of the front of card 4

Card 5

Front

What is the resultant force?

Back

Preview of the front of card 5
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