define force
- a push or pull that tends to alter the state of motion of a body
- f = ma
what happens when two forces act?
- the effect of forces acting in the same direction is combined
- forces opposing each other have a cancelling effect
what are balanced forces?
when two or more forces acting on the body are equal in size but opposite in direction so cancel out and produce a net force of 0
what are unbalanced forces?
when two or more forces acting on a body do not cancel out, meaning a net force acts
define net force
the overall force acting on a body when all forces are considered, also known as the resultant force
what are the vertical forces?
- weight: the gravitational pull that acts downwards from the body’s centre of mass
- reaction: equal and opposite to the action force and acts upwards from the point of contact w/ the ground
define friction
the force opposing the sliding motion of one surface across another
what are the factors that affect friction?
- characteristics/roughness of surface 1 & 2
- weight/normal ground reaction force
- temperature e.g. heated tires
how can friction be maximised?
- increasing the roughness of either of the surfaces e.g. dimpled netball
- increasing the mass/ normal reaction force
- increasing the temperature e.g. using tyre heaters
how can friction be minimised?
increasing the smoothness of surfaces e.g. wax skis, melt and refreeze ice rinks
define air resistance
the force acting to oppose the motion of a body through air
what factors affect air resistance?
- velocity
- frontal cross-sectional area
- streamlining and shape
- surface characteristics
- air density/altitude
how can we minimise air resistance?
- reducing frontal cross-sectional area: skier adopts a crouched position
- using a streamlined shape: ski jumper in flight has an aerofoil shape
- making surfaces smooth: cycling helmets and suits designed to minimise turbulence
define momentum
- the amount of motion possessed by a moving body
- = mass x velocity (Kgm/s)
define acceleration
- the rate of change in velocity
- = f/m OR change in velocity/ time
define weight
- the (gravitational) force that earth exerts on the mass of the body
- weight = m x g (g=10 m/s/s) (kg)
define velocity
- the rate of change of displacement
- v = displacement/time taken (m/s/s)
define streamlining
the creation of smooth air flow around an aerodynamic shape to minimise resistance
