Science - Force
What is a force?
This is something that can change the motion of an object
State the SI unit for force
The SI unit for force is the newton (N)
How is force measured?
Force is measured using a spring balance
Explain what forces can do
They can change the speed of an object
They can change the shape and size of an object
They can change the direction an object is moving in
What is meant by contact forces?
These are two objects that have to be in contact for these forces to occur eg. push, pull, friction and tension
What is meant by non-contact forces?
These are two objects that do not have to be in contact for these forces to occur eg. gravity
Explain centre of gravity
This is the point where the object balances
What does an object need to have in order for it to be in stable equilibrium?
A wide base
A low centre of gravity
What is meant by equilibrium?
This is when all the forces are balanced in a body
What is meant by stable?
This is when an objects centre of gravity is inside the base of the object
What is meant by unstable?
This is when an objects centre of gravity is outside the base of the object
What is meant by neutral?
This is when an objects centre of gravity does not change
What is a fulcrum?
This is the turning point of an object
What is a lever?
This is any rigid body that rotates (free to move) about a fixed point called a fulcrum eg. see-saw
Explain the law of the lever?
This states that the sum of the clockwise moments equals the sum of the anticlockwise moments
What is meant by a moment of a force?
This is the rotation about the fulcrum
This is a force the opposes motion when two objects are place in contact
State an advantage of friction
It allows us to have grip when you walk, run and climb or when you alloy the brakes on a bike or in a car
State a disadvantage of friction
Wears away the soles of our shoes
Wears away the tyres on our car and bicycles
Explain how to reduce friction
Lubrication is used to reduce the friction between two solids eg. oil and wax
Surfers wax their surfboards to reduce the friction between the board and the water
What are elastic objects?
This is any object that is able to restore its shape after it has been stretched or compressed eg. springs and elastic bands
What is meant by elastic limit?
This is when elastic objects are extended to a point where they will not restore their shape
Explain Hooke's Law
This states that the extension of a spring is directly proportional to the applied force
This is because the points give a straight line through the origin
Science - Force