Force And Work Flashcards
Measuring force
Unit : Newton (N)
Named after Sir Isaac Newton
1 N is approx the force needed to support an apple.
Measured using Newton-meter or Spring balance
Weight
The weight of an object is the force of gravity on it.
Pull of the earth is stronger at the poles.
Weight of an object on the moon is a sixth of what it is on earth.
Weight and mass
We mix up the two.
A weighing scales gives the mass of an object.
Mass is measured in kg.
Weight is a force and is measured in newtons.
Acceleration
Acceleration due to gravity is approx 10 m/s2
How to find weight (in newtons)
Multiply mass (in kg) by acceleration due to gravity (10 m/s2)
Force
A force is something that causes an object to accelerate
Friction
Friction is a force which opposes motion between two objects in contact.
Disadvantages of friction
Friction slows things (why ships travel slower than planes).
Friction results in waste of energy (food mixers and car engines produce a lot of unwanted sound and heat energy).
Friction wears away surfaces in contact with each other (tyres lose their thread and brake pads on bicycles wear away).
Advantages of friction
It slows things down (brakes in a car or bike).
Friction between the road and wheels allow the thing to move. It allows us to walk.
Friction allows us to write and pick things up.
Lubrication reduces friction
Oil and grease are lubricants.
Stretching forces
Said to be elastic.
When a force is put on them they change shape.
When the force is removed they return to the original shape
Hookes law
The extension of a spring is directly proportional to the force that is stretching it
Work
Work done = force x distance moved
Measured in joules. Distance moved is measured in metres.
E.g. swimming
Energy
Energy is the ability to do work.
Power
Measure of how quickly work is done. Energy used per second. Power is the work done per unit time. Power = work done/time taken Measures in watts
