Physics Key Points
A force can do one of four things to an object: 1. Make it speed up - accelerate.
2. Make it slow down - decelerate.
3. Change its direction.
4. Change its shape.
If something is doing one of these four things there must be net force acting upon it.
Newton's First Law
'Every body continues in a state of rest or uniform motion unless acted upon by an external force.'
Something without net force acting on it will either stay still or move at a constant speed in a straight line until you apply a force to it.
F = ma
Newton's Second Law:
• F is the force in Newton’s, N.
• m is the mass in kilograms, kg.
• a is the acceleration in m/s2.
This shows that if you keep the mass constant and double the applied force the acceleration will double.
Hooke's Law, elastic and plastic behaviour
F = kx
An elastic material is one that will return to its original shape when the force applied to it is taken away.
A plastic (or inelastic) material is one that stays deformed after you have taken the force away.
If you apply too big a force a material will lose its elasticity.
In solids
If a force is applied over a smaller surface area you get a larger pressure.
Pressure can be calculated using the following equation:
Pressure = force/area
Force will be in Newton’s, N.
Area will be in either m2 or cm2.
If the area is in m2 then the pressure will be measured in Pascal’s or N/m2.
If the area is in cm2 then the pressure will be in N/cm2.
In liquids
1. Pressure increases with depth.
2. Pressure acts equally in all directions.
3. Pressure is transmitted through liquids.
Hydraulics
All hydraulics systems work because the pressure is the same throughout the system.A really good example of this is a car brake system. You need to know all about this for your exams.
In gases
Although gases are compressible (squashy) they exert a pressure because of the gas particles bouncing off things.
Boyle's Law
For a fixed mass of gas the
2. Make it slow down - decelerate.
3. Change its direction.
4. Change its shape.
If something is doing one of these four things there must be net force acting upon it.
Newton's First Law
'Every body continues in a state of rest or uniform motion unless acted upon by an external force.'
Something without net force acting on it will either stay still or move at a constant speed in a straight line until you apply a force to it.
F = ma
Newton's Second Law:
• F is the force in Newton’s, N.
• m is the mass in kilograms, kg.
• a is the acceleration in m/s2.
This shows that if you keep the mass constant and double the applied force the acceleration will double.
Hooke's Law, elastic and plastic behaviour
F = kx
An elastic material is one that will return to its original shape when the force applied to it is taken away.
A plastic (or inelastic) material is one that stays deformed after you have taken the force away.
If you apply too big a force a material will lose its elasticity.
In solids
If a force is applied over a smaller surface area you get a larger pressure.
Pressure can be calculated using the following equation:
Pressure = force/area
Force will be in Newton’s, N.
Area will be in either m2 or cm2.
If the area is in m2 then the pressure will be measured in Pascal’s or N/m2.
If the area is in cm2 then the pressure will be in N/cm2.
In liquids
1. Pressure increases with depth.
2. Pressure acts equally in all directions.
3. Pressure is transmitted through liquids.
Hydraulics
All hydraulics systems work because the pressure is the same throughout the system.A really good example of this is a car brake system. You need to know all about this for your exams.
In gases
Although gases are compressible (squashy) they exert a pressure because of the gas particles bouncing off things.
Boyle's Law
For a fixed mass of gas the