# P4 - Explaining Motion

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Forces always arise in pairs? What are both parts called?
equal and opposite
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What are contact forces? Give examples
Most forces are contact forces, where thing shave to make contact for a force to be present. eg swimmer and water, jumper and ground, propeller and air
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What are non-contact forces? Give examples
Forces that don't require any contatc to act. e.g gravity and magnets
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How many things do you need for a force to happen?
2
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What is friction?
When the tiny microscopic imperfections in forces get stuck and caught on each other. They will eventually move when they break off and wear down, or mov eover them
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What way does friction work in relation to the force?
Friction always works in the opposit eway to the dirction of the force.
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Why do liquids make less friction?
Liquids make less friction becase they fill in the gaps of the surface so th etiny imperfections caan't get caught on each other as the liquid is trapped in the middle.
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What is the difference between speed and velocity?
Speed is a measure of how far you travel over a set period of time and velocity is pseed with a direction of travel?
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What equation that links speed, distance and time?
Speed=Distance/Time
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I travel 8 miles in 15 minutes what speed am I travelling at?
15x4=60mins=hour......8x4=24mph
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What is acceleration? What is its unit?
How quickly you are speeding up - How much faster you are going each second - m/s/s
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What is the difference between a distance time graph and a displacement time graph?
A displacement time graph is how far you are away from the start point at any time wheras a distance time graph is the total distance you have travelled and there are no negatives. A disaplacement time graph can have negatives - travel back to start
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What does a upwards curve on a distance time graph show?
Acceleration
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What does a horizontal line on a distance time graph show?
No movement - a stop
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What does the gradient represent in a velocity time graph?
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What is a reaction force?
When a force happens because of sometthing being acted upon it. eg a book on a table, the book's force on the table is weight. The equla and opposite forces are from the table upwards on the book. Its a reaction because it reposnds to the force.
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If there are two arrows of the same size in the opposite direction on an object, what is the motion of the object?
Stationary because the forces are equal.
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What is a resultant force?
The overall force acting upon the object. If one arrow is bigger than the other in the opposite direction then this is the resultatnt force
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Are forces balanced when something is accelerating?
No, because if they were balanced then it wouldn't be getting faster. The bigger the resultant force, the bigger the acceleration.
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What is momentum?
How hard it is to stop moving. The heavier the object, the faster it is the harder it is to stop.
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What type of quantity is momentum?
A vector quantity - it has size and direction
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A 64kg giraffe is moving at 10m/s. What is its momentum?
momentum=massxvelocity.....momentum=64x10=640 kg m/s
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What is the unit for momentum?
kg m/s
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What is the unit for weight?
N
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What is the unit for mass?
g or kg
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What happens when a resultant force acts upon a object?
It causes a chnge in momentum in the direction of the force
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change in momentum = ?????????????x???????????//
momentum = resultant force x time for which it acts
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What do car safety features do?
Bring you or part of you to a stop over a longer period of time.
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Give examples of car safety features.
Air bag, crumple zone, seatbelts.
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What is GPE?
Gravitational Potential Energy - the energy in something that is raised against energy. if yoou lift and object kinetic energy changes into GPE, and if it falls GPE decreases and kinetic energy increases
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Kinetic Energy gained = ..........................?
Kinetic energy gained = Gravitational Potential energy lost.
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How many newtons is 1kg on Earth?
10
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What is work done?
The amount of energy transferred
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P4
P4
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Velocity=................?
Velocity = squareroot(kinteic energy/half mass)
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kinetic energy=................?
1/2 mass x velocity^2
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A man leans on a wall with a force of 50N. What can you say about the force exerted by the wall?
It is a reaction force of 50N on the mannn otherwise he would fall through the wall
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A crazy dog dragged a big branch 12m over next door neighbours front lawn, pulling with a force of 535N. How much work has done on the branch?
work done by a force = force x distance moved in the direction of the force......work done = 12x535=6420J
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## Other cards in this set

### Card 2

#### Front

What are contact forces? Give examples

#### Back

Most forces are contact forces, where thing shave to make contact for a force to be present. eg swimmer and water, jumper and ground, propeller and air

### Card 3

#### Front

What are non-contact forces? Give examples

### Card 4

#### Front

How many things do you need for a force to happen?

### Card 5

#### Front

What is friction?