# Physics P4

• Created by: Pedley98
• Created on: 02-06-15 14:58
Definition of Speed
How far an object will travel in a certain time.
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Definition of Velocity
Objects speed and gives an indication of its direction of travel
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To calculate speed we need to know 2 things:
the distance it has travelled and the time it took to travel that distance
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Definition of instaneous speed
Speed of an object at a particular point in time.
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What does distance-time graph show
Distance travelled by an object changes with time
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What does a steep gradient indicate
The steeper the slope the greater the speed
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What does a straight line represent on a distance time graph
Staionary object
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What does a horizontal line with a gradient represent on a distance time graph
Moving at a constant speed
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How do you calculate speed
speed= distance travelled divided by time taken
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When the gradient is changing what does that indicate
The objects speed is changing
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Definiton of acceleration
Rate at which its velocity changes.
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What does a steep slope on a speed time graph indicate
The steeper the slope the greater the acceleration
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What does a velocity-time graph show
It shows the velocity at which an object is moving changes with time
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What does moving in a straight line mean on a velocity time graph
its a positive velocity
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How does a force occur
A force occurs when two objects interact with each other
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Definition of an interaction pair
Forces are equal in size and opposite in direction
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What forces only occur because of a response of another force
Friction and reaction of a surface
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What is the reaction of a surface
It is when an object is being pulled down to the surface by gravity and the surface pushes up with an equal force called the reaction of the surface
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What is friction
When 2 objects try to slide past each one another, both objects experience a force that tries to stop them moving
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What is a resultant force
The overall effect of adding all these forces, taking direction into account
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What 2 forces experence when objects fall
The downward force of the weight and the upward force of air resistance
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What happens when a skydiver jumps out of a plane
The speed of his descent can be considered in two seperate parts
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When the parachute opens
He initially accelerates due to the force of gravity
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When he carries on falling what happens
He experiences the force of air resistance but it is not as great as the weight so he continues to acclerate
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What happens as his speed increases
The air resistance acting on him, until eventually the resistance is equal to weight
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What does this do to the resultant force
The resultant force reacting on him is now zero and his falling speed becomes constant
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What happens after the parachute opens
Unbalanced forces act again because the upward force of resistance is now greatly increased and is bigger than weight
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What occurs after the parachute opens
This decreases the speed and his speed decreases so does resistance
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What happens as the skydiver reaches the ground
Eventually the resistance decreases until it is equal to weight, he falls at a steady speed , slower than before though until he lands on the ground
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What is momentum
It is a measure of an object
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What is change in momentum?
If the resultant force actibg on an object is zero its momentum will not change
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If an object is stationary
It will remain stationary
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The size of the change in momentum depends on
The size of the resultant force and the length of time the force is acting on the object
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What occurs in a collison
During a collision it comes to a sudden stop it undergoes a change in momentum
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What is a crumple zone
An area desgined to crumple on impact, it helps to increase the time during the car changes momentum
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When does an object have kinetic energy?
When an object is moving
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The amount of kinetic energy depends on
The mass of the object and the velocity of the object
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The greater the velocity of an object means that...
The more kinetic energy it has
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What is gravitational potential energy
As an object lifts above the ground it gains GPE
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What happens when an object falls
Its GPE decreases and it is converted into kinetic energy
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When is work done
When a force moves and object work is done on the object resulting in the transfer of energy
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What happens when work is done on an object
It loses energy and when work is done on an object it gins energy according to the relationship
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What happens when a car is travelling at a constant speed
the driving force from the engine is balanced by the counter force
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What is the equation for work done
Work done= force X distance moved by the force
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## Other cards in this set

### Card 2

#### Front

Definition of Velocity

#### Back

Objects speed and gives an indication of its direction of travel

### Card 3

#### Front

To calculate speed we need to know 2 things:

### Card 4

#### Front

Definition of instaneous speed

### Card 5

#### Front

What does distance-time graph show