Chapter 4 Force and Work:
Points to Note:
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A force is something that causes an object to change velocity or to accelerate
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The unit of force is the newton (written N).
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Forces can be measured using a spring balance or a newton meter
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The weight of an object is the force of gravity on it
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Mass is the quantity of matter in an object and is measured in kg's
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Weight is a force. We can prove this as the it is the force of gravity which causes an object to have weight and thus accelerate towards the Earths surface
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Weight in newtons = Mass (kg's) x 10
Left: Newton meters used to measure force
Right: A picture explaining how newton came to disocver the force of gravity
Friction as a Force:
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Friction is a force that opposes motion between two objects in contact
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For example if you hit a puck along the road it will stop quite quickly due to the frcition between the road and the puck
Friction is a nusaince Force as:
1. Friction often slows things down e.g ice puck slowed down by friction
2. Friction wears away surfaces in contact with each other. For example tyres lose their thread due to the constant contact with the ground
Methods of Preventing Friction:
1. Lubrication oil can be used in engines to stop moving parts constantly moving against each other and wearing down as a result
2. Ball bearings to reduce the friction between the wheel and its axel
Friction as a useful force:
1. Without friction between a car and the road a car would not move
2. We also use friction to help stop or slow down certain things such as the brakes of a car or bicycle
Stretching Force:
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Take for example a bed, when pressure is put on the bed the strings change shape but when this pressure is removed the springs return to their original shape. Objects like this are said to be elastic
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So a suitable definition for something elastic would be: An object which is capable of reverting back to its original shape after it had been changed due to pressure
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Hookes law states that the extension of a spring is directly proportional to the force that is stretching it
Left: Lubrication oil is commonlt used to prevent the wearing down of parts
Right: When we think of elastic, elastic bands often come to mind
Work, Power and Energy
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In English work means a task or a duty in science it only means one thing-"Work is done only when a force moves an object"
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Work Done= Force x Distance moved and work done is measured in joules
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For example, when you go up a flight of stairs you are doing work as you are moving a force (your weight) a certain distance
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However, when you run up the stairs you are using more power as the time you are doing the work in is decreased
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Power is defined as the energy used per second and is measured in watts
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The formula for Power is work done divided by time taken to do that work
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Energy however is the ability to do work or move something
