Answers to ‘Revise as you go’
1. Define linear, angular and general motion and give a sporting example for each type.
Linear motion
When a body moves in a straight or curved line, with all its parts moving the same distance, in the same
direction and at the same speed, e.g., remaining in the crouched position in downhill skiing; the flight
path of a shot put; etc.
Angular motion
When a body or part of a body moves in a circle or part of a circle about a particular point called the
axis of rotation, e.g., the action of the arm around the shoulder joint when bowling in cricket; the action
of the leg about the hip joint in running; the action of a male gymnast about the bar in the Olympic high
bar event; etc.
General motion
A combination of linear and angular motion, e.g., sprinting 200m; dribbling a ball down the basketball
court; swimming 50m; etc.
2. Define force and list four effects that a force can have on a body. Apply each of these four
effects to a sporting example.
Force
A push or a pull that alters, or tends to alter, the state of motion of a body.
A force can:
cause a body at rest to move
e.g., a swimmer on the blocks at the start of a race needs to apply a force on the blocks to initiate the
dive on the gun.
cause a moving body to change direction
e.g., a swimmer applies a force on the wall during the tumble turn to change direction and swim back the
other way
cause a moving body to accelerate
e.g., in a tight race to the wall, a swimmer can apply a greater force to the water to increase their speed
in an attempt to win the race
cause a moving body to decelerate
e.g., the force applied by the head of the swimmer on the wall at the end of the race will cause them to
stop
cause a body to change its shape
e.g., the force applied by the swimmer when entering the water after the dive causes a disturbance to
the water.
3. Apply each of Newton’s Laws of Motion to a sporting example of your choice.
Newton’s First Law
A sprinter will remain in the “set” position on the blocks until they apply an external force to change
their state of motion.
Newton’s Second Law
The greater the force the sprinter applies to the blocks, the greater their acceleration out of them at
the start of the race.
Newton’s Third Law
The sprinter applies a force with their feet backwards and downwards on the blocks and the blocks
apply an equal and opposite force, forwards and upwards, on the athlete, allowing them to move.
4. What do you understand by the terms centre of mass and line of gravity?
Centre of mass
The point at which the body is balanced in all directions.
Line of gravity
An imaginary line extending from the centre of mass vertically down to the ground.
5. Why is the position of the centre of mass higher in males than females?
The centre of mass is not a fixed point.
Its location varies depending on the spread of mass of the body.
Males tend to have more mass concentrated at their shoulders and upper body.
Females tend to have more mass concentrated at their hips, therefore a male’s centre of mass is higher
than a female’s.
6. Explain how the position of the centre of mass can lie outside the mass of a body and give
examples from sport of when this is the case.
As soon as an athlete moves position, their centre of mass also shifts to find that unique position of
balance for that particular body shape.
In extreme body shapes where much of the mass of the body is concentrated in front of the hips, the
position of the centre of mass can actually move outside the mass of the body, e.g., pike jump in
trampolining/diving, bridge in gymnastics, Fosbury flop in high jump.
7. List four factors that affect the stability of a body. Give sporting examples of a stable
position and an unstable position.
position of the body’s centre of mass – lower = more stable
size of a body’s base of support – large = more stable
position of a body’s line of gravity – closer to the centre of their base of support = more stable
mass – larger = more stable
body position in relation to oncoming force – leaning into force = more stable
example of stable body position = “on your marks” position in the sprint start
example of unstable position = just after “bang” in sprint start position when the hands have left the
track surface
8. Explain the relationship between centre of mass and force in producing (a) linear motion and (b)
angular motion.
a) To produce linear motion, the line of action of the force must pass through the body’s centre of mass.
This is known as a direct force.
b) To produce angular motion, the line of action of the force must pass outside the body’s centre of
mass. The further the line of action from the centre of mass, the greater the rotational effect. This is
known as an eccentric force.
9. Explain why a handstand is a more demanding balance than a headstand.
A handstand is a more unstable balance, therefore more difficult to hold.
This is because:
the centre of mass in the handstand is higher than in the headstand;
the size of the base of support in the handstand is smaller than in the headstand;
the position of the line of gravity is more likely to fall outside the base area in a handstand than
in a headstand, leaving less margin for error;
when the line of gravity falls outside the base of support the body becomes unstable.
10. Describe the varying degrees of stability on a performer carrying out the three stages of a
sprint start, “on your marks”, “set”, “bang!”
“on your marks”
most stable position
the position of the centre of mass is at its lowest
the base of support is large (four points of contact)
the line of gravity is at its closest to the centre of the base of support
“set”
less stable than “on your marks” position
the position of the centre of mass has raised slightly
the size of the base of support has not changed (four points of contact)
the line of gravity has moved forward to be very close to the front of the base of support (the line of
the hands)
because the line of gravity remains within the base of support, the body is still stable in this position
“bang!”
unstable position
the position of the centre of mass has raised again
the size of the base of support has decreased (one/two points of contact)
the line of gravity now lies outside the base of support
the athlete must start to move their legs to find a new position of stability
Answers to ‘Revi