Force

Question 1

define force

Answer 1

a push or pull that tends to alter the state of motion of a body
- f = ma

Question 2

what happens when two forces act?

Answer 2

• the effect of forces acting in the same direction is combined
• forces opposing each other have a cancelling effect

Question 3

what are balanced forces?

Answer 3

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

Question 4

what are unbalanced forces?

Answer 4

when two or more forces acting on a body do not cancel out, meaning a net force acts

Question 5

define net force

Answer 5

the overall force acting on a body when all forces are considered, also known as the resultant force

Question 6

what are the vertical forces?

Answer 6

• 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

Question 7

define friction

Answer 7

the force opposing the sliding motion of one surface across another

Question 8

what are the factors that affect friction?

Answer 8

• characteristics/roughness of surface 1 & 2
• weight/normal ground reaction force
• temperature e.g. heated tires

Question 9

how can friction be maximised?

Answer 9

• 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

Question 10

how can friction be minimised?

Answer 10

increasing the smoothness of surfaces e.g. wax skis, melt and refreeze ice rinks

Question 11

define air resistance

Answer 11

the force acting to oppose the motion of a body through air

Question 12

what factors affect air resistance?

Answer 12

• velocity
  -frontal cross-sectional area
• streamlining and shape
• surface characteristics
• air density/altitude

Question 13

how can we minimise air resistance?

Answer 13

• 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

Question 14

define momentum

Answer 14

the amount of motion possessed by a moving body
- = mass x velocity (Kgm/s)

Question 15

define acceleration

Answer 15

the rate of change in velocity
- = f/m OR change in velocity/ time

Question 16

define weight

Answer 16

the (gravitational) force that earth exerts on the mass of the body
- mass = m x g (g=10 m/s/s) (kg)

Question 17

define velocity

Answer 17

the rate of change of displacement
- v = displacement/time taken (m/s/s)

Question 18

define streamlining

Answer 18

the creation of smooth air flow around an aerodynamic shape to minimise resistance