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

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.

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.

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
    

    

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