- Created by: Glendia
- Created on: 21-08-17 10:15
Introduction To Forces
- Forces are vector quantities- they include magnitude and direction.
- Forces are either:
- Contact Forces- the objects are actually touching, e.g. friction, tension, upthrust and drag
- Non-contact Forces- the objects are not touching, e.g. Gravitational, electrostatic and magnetic force
- These can be shown on a free body diagram
- Resultant Force: the total force acting on an object, as a result of many forces.
- These can be shown on vector diagrams
Forces and Elasticity
An object changes shape when more than one force is applied onto it.
- It was elastically deformed, if it returen to original shape.
- It is inelastically deformed, if it does not return to original shape.
The extention/compression of the object is directly proportional to the force applied until it reaches the limit of proportionality. This is shown in the force-extension/compression graph:
The work done to stretch/compress object is equal to the elastic potental energy in object.
Moments, Levers and Gears
A moment is when a force causes an object to rotate aroud a pivot point.
- If the object is balanced:
- the total clockwise moment is equal to the total anti-clockwise moment.
- F1 x d1 = F2 x d2
- When the applied force > transmitted force, the distance is increased.
Pressure in a Fluid
A fluid can be liquid or gas.
- When particles in a fluid collide with a surface (partical or container surface), they exert force.
- Pressure is force per unit area.
- Small area = large pressure -> force created is larger
- Large area = small pressure -> force created is smaller
Pressure at Depth
The lower the height means the greater the pressure.
- This is because there are more particles above you, so the force is greater.
- This applies to atmospheric pressure as well as pressure in a liquid.
The pressure at a particular point in a column of liquid is greater when:
- The higher the column and the denser the liquid
Upthrust is created when the pressure at the bottom surface of an object > the pressure at the top surface of an object.
- This happens in a liquid because:
- there are more particles underneath object than above.
- Therefore the resultant force is upwards.
- An object floats when: force = upthrust, and sinks when: force > upthrust
- An object less dense than the liquid will:
- displace a volume of liquid greater than its weight, so it will rise
- the less dense the object, the more will remain above surface.
- An object denser than the liquid, cannot displace enough liquid equal to its own weight, so it sinks.The size of upthrust = weight of water displaced