Ocr Additional Science Higher - Physics, P4 Forces in motion

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• Created by: Marwa
• Created on: 22-04-12 13:30

## Interacting Forces

A force happens when two objects (called „bodies‟) ____with each other, this is called an _____ _____ . Whenever an object ____ a force on another object, it always feels a force equal in ___ and opposite in ____ to the one that it exerts. This was discovered by the English scientist _____ _____.

A good example of this is two people floating in a swimming pool. If the first person pushes the second person, both people will ____ ____ from each other in ______ directions.

The biggest force that you are currently feeling is the force of _____. Gravity is a ______ force. Gravity pulls you towards the Earth, but you are also pulling the Earth towards you! So not only do forces _____ they can also pull. Magnetism is a similar force which can pull objects together.

Answer: interact, interact, exerts, interact, direction, Isaac Newton, Move away, opposite, Gravity, Pulling, Push

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## Moving around

When a rocket takes off its engines burn fuel (oxygen and hydrogen) and the gas produced is _____ _____ of the ____ of the rocket. A force then happens in the ______ ______ pushing the rocket up into space. A jet engine on a plane works in a similar way by sucking in ___ and pushing it out the ___. Jet engines can’t work in space as there is ____ ____.

Cars move by the engine turning the wheels, which exert a force on the ___ and makes the car move _____. If the road is very slippery and the tyres can not grip the road, then the wheels will simply spin around and the car will not move. The car can’t exert a force on the road.

______ is a force which prevents objects sliding past each other. When a car has a good grip of the road the wheel turns and pushes _____, exerting a force against the road. There is then a force of ____ size in the ____ direction from the road, which pushes the car forwards. The interaction pair is made up of the wheel and the road.

Answers: Pushed out, Bottom, opposite direction, air, back, no air, road, forward, Friction, Back, equal, opposite, forward

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## Reaction of surfaces

If you are holding your MP3 player and drop it, the MP3 player will move _____ and hit the ground. The force of ____ from the Earth will pull the MP3 player downwards.

Now if you place your MP3 player on a table then the table will hold the MP3 player up, it will not fall to the ground. Gravity is still pulling the MP3 player ______, but there must be a force holding the MP3 player up. The table is producing a force of ___ ___ and in the ____ direction to the pull of gravity, and the two forces balance each other out. This is called the reaction of the surface.

Answers: Downwards, gravity, downwards, equal size, opposite

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## Combining Forces

Everything on Earth weighs something, but your weight depends upon where you are in the universe. Weight is actually a _____ and is the combination of your mass (the stuff you are made of), and the pull of gravity (the gravitational field strength)

You may have heard scientists say that in space you are ‘weightless’, and this is because there is no ____ to pull you down. This doesn’t mean that you have no mass, as you still exist, it just means that your body is not feeling the pull of gravity. Weight is measured in ____ (__).

If there are ___ acting on an object but the object is not moving then the forces must be _____. In other words the forces are ____ __ ___ ___ and so the overall force is 0. If there are two forces acting on an object they can either:

1. Add up: If the forces are acting in the same direction.

2. Subtract: If the forces are acting in opposite directions.

Answers: Force, Gravity, newtons, N, forces, balancing, cancelling each other out.

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## The need for Speed

People often talk about speed, when they talk about cars and planes and other modes of transport. In the Beijing Olympics everyone was talking about Usain Bolt and his speed when he won the 100m and 200m sprints. The ____ ____ tells us how far an object travels in a certain amount of time. To calculate speed we need to know two things:

1. The _____ travelled.

2. The time it took to travel that distance.

Sometimes we want to know the ____ at a particular point in time. You may have noticed that cars contain speedometers, and this tells us how fast the car is moving at a certain point in time. This is called the _______ speed.

Answers: Average Speed, Distance, speed, instantaneous

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## Momentum

If you push a ______ object, for example a toy car, it will start moving. The force from the push has given the toy car ____or _______. Momentum is a measure of the ____ of an object and can be calculated using the equation:

Momentum (kg m/s) = Mass (kg) × Velocity (m/s).

Since you are using ____, momentum also tells us what _____ that an object is ____ in. For example, if you push the car left to right, then its velocity is ____. If you push the car right to left, then its velocity is in the opposite direction and will be ____.

The ______ of an object can be changed by ______ a force on it. As long as the ______ force (overall force) is greater than zero it will cause a change in the momentum in the direction of the force.

Answers: Stationary, motion, momentum, motion, velocity, direction, travelling, positive, negative, momentum, exerting, resultant

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## Crashing a car

Designers are constantly trying to find ways that they can make the duration of a crash ___ ____. Cars now have various safety features so that they protect the people travelling inside, such as seat ___ and ____ ____.

A crumple zone is an excellent invention as it ______ the duration of the crash, ______ the ______force that the car and passengers feel.

Answer: Last Longer, belts, crumple zones, increases, reducing, resultant

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When you are in a car or on a bike, the engine of the car, or the cyclist, will be producing a force to keep the object moving forward. This is called the ___ ____. If you think about this with a car, the ____ is causing the wheel to turn, which ____ against the ground. The ground then produces a force on the tyre which _____the car forward. The ____ is what is causing the force which allows the car to move ____.

The ___ ___ is not the only force that is acting upon the car though, there will be forces acting upon the car to slow it down:

1. Air resistance: As any object moves through the air, the air will actually ___against the object, producing a force that __ the object down. This is why cars are designed to be aerodynamic, to cut __ the air resistance.

2. Friction: When the car’s wheels move upon the axle, the movement is not perfect and some of the ___ is lost as heat and sound. This will cause the object to ___ ___ . This is why axles on cars and bikes are oiled, to cut down the amount of friction.These are called ___ forces and they act in the ____direction to the driving force.

Answers : Driving Force, engine, Pushes, pushes, engine, driving force, push, slows, down, energy, slow down, counter, opposite

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## work done & energy

Unfortunately you might at some point be driving a car and it will break down. If you are in the middle of nowhere this could be a problem as you might need to push the car to a garage to get the car fixed.

To push the car you will need to do some ___, and this means ____ energy from you to the car.

 When an object does work it __ energy.

 When work is done on an object it ___energy.

This means that the person pushing the car is doing work and __ energy. The car is having work done on it and is gaining energy to get the car moving.

The ____ __ ___ you will do pushing the car will be ___ to the amount of energy you will transfer to the car. This means that if you do 100,000J of work to push the car, then the car will have ___ 100,000J.

answers: work, transferring, loses, gains, losing, amount of work, equal, gained

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## Potential and Kinetic Energy

Whenever you pick up an object off the floor, such as a book, and place it on a table, you are doing work. The book has had __ ___ on it and this has become ____ _____ _____ (__). It is called potential energy as there is energy stored in the book, which has the potential to become other types of energy. The GPE is ____ to the amount of work you have done.

Whenever you ___ an object along the ground, for example pushing a broken down car along the road, you are ____. You are ____ energy from you to the car, causing the car to speed up. The car now has _____ energy and this is called ______ _____ (_). The amount of kinetic energy that the car gains is equal to the ____ you have  ____.

It is important to know that ____ ____ ____can become kinetic energy. A simple example to think of is the book that we placed on the table. If the book is knocked off the table, it will ____ gravitational potential energy, as its height decreases, but its kinetic energy will ___ as it speeds up. GPE lost = KE gained This is called the principle of conservation of energy, as energy is changed from one form to __.

Answers: Work done, gravitational potential energy, (GPE), Push, working, transferring, moving, kinetic energy, (KE), work , done, gravitational potential energy, lose, increase, another.

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