Biomechanical Principles - Newtons Laws, Forces, Free body diagrams, Stability

Question 1

What are Newton’s 3 laws of motion?

Answer 1

1 - Law of inertia
2 - Law of acceleration
3 - Law of reaction

Question 2

Describe Newtons 1st Law

Answer 2

The law of inertia states that a body will remain at rest of constant speed unless acted upon by an external or unbalanced force.

Question 3

Describe Newtons 2nd Law

Answer 3

The law of acceleration states that a body’s rate of change in momentum is proportional to the size of force that acts on it, in the same direction as the force applied.
(the bigger the force applied, the faster the acceleration/speed)

Question 4

Describe Newtons 3rd Law

Answer 4

Newtons law of reaction states that for every reaction there is an equal and opposite reaction.

Question 5

Give a sporting example of Newtons 1st Law

Answer 5

A football won’t move unless it is moved by an external force ( a foot kicking it)

Question 6

Give a sporting example of Newtons 2nd Law

Answer 6

The bigger the force applied to a sprinter when they start moving, the faster they will accelerate from the blocks.

Question 7

Give a sporting example of Newtons 3rd Law

Answer 7

The force a high jumper applies into the ground to take off will be equal and opposite direction to push them up in the air.

Question 8

What is a force?

Answer 8

A push or pull that alter the state of motion in a body.

Question 9

How do you calculate force?

Answer 9

Force = mass x acceleration

Question 10

What is force measured in?

Answer 10

Newtons ( N )

Question 11

What does the term net force mean?

Answer 11

The sum of all forces acting on the body/ the overall force acting on the body when all forces have been considered.

Question 12

What is meant by the term ‘balanced force’?

Answer 12

A balanced force occurs when 2 or more forces acting on a body are equal in size and opposite in direction.

Question 13

What is meant by the term ‘unbalanced force’?

Answer 13

An unbalanced force occurs when two forces are unequal in size and opposite in direction.

Question 14

On a free body diagram, what are the two vertical forces?

Answer 14

Weight - Downwards
Reaction - Upwards

Question 15

On a free body diagram, what are the two horizontal forces?

Answer 15

Friction ( forwards )
Air Resistance ( backwards)

Question 16

What is weight?

Answer 16

The gravitational pull that the earth exerts on a body.

Question 17

What is reaction?

Answer 17

The equal and opposite force exerted by a body in response to the action forces places upon it.

Question 18

What is friction?

Answer 18

The force that opposes the motion of two surfaces in contact.

Question 19

What is air resistance?

Answer 19

The force that opposes the motion of a body travelling through the air.

Question 20

Where do you draw the weight arrow from on a free body diagram?

Answer 20

The centre of mass downwards

Question 21

Where do you draw the reaction arrow from on a free body diagram?

Answer 21

The points in contact with the floor going upwards

Question 22

Where do you draw the friction arrow from on a free body diagram?

Answer 22

The points in contact with the floor going forwards

Question 23

Where do you draw the air resistance arrows from on a free body diagram?

Answer 23

The centre of mass, backwards

Question 24

What does it mean if the weight arrow is bigger than the reaction arrow

Answer 24

Weight is bigger than reaction, therefore you are moving downwards / squatting

Question 25

What does it mean if the reaction arrow is bigger than the weight arrow?

Answer 25

Reaction is bigger than weight, therefore you are moving upwards ( but still in contact with the floor) - taking off for a jump

Question 26

What does it mean if the friction arrow is bigger than the air resistance arrow?

Answer 26

You are accelerating

Question 27

What does it mean if the air resistance arrow is bigger than the friction arrow?

Answer 27

You are decelerating

Question 28

What does R>W mean?
Give a sporting example to show when it might occur.

Answer 28

Reaction is bigger than weight.
A basketball player is moving upwards during the take off for a slam dunk

Question 29

What does R<W mean?
Give a sporting example to show when it might occur.

Answer 29

Reaction is less than weight.
A weight lifter is moving downwards in a squat.

Question 30

What does F>AR mean?
Give a sporting example to show when it might occur.

Answer 30

Friction is less than air resistance.
A sprinter is accelerating off the blocks

Question 31

What does F<AR mean?
Give a sporting example to show when it might occur.

Answer 31

Friction is less than air resistance.
A sprinter slowing down age crossing the finish line

Question 32

What does R=W mean?
Give a sporting example to show when it might occur.

Answer 32

Reaction is equal to weight.
There is no vertical movement to an action, e.g. a 1500m runner is moving forwards

Question 33

What does F=AR mean?
Give a sporting example to show when it might occur.

Answer 33

Friction is equal to air resistance.
A marathon runner is a t constant velocity or standing still. (there is no, or constant, horizontal movement in action)

Question 34

Describe the term ‘centre of mass’

Answer 34

The point at which a body is balanced in all directions.

Question 35

What is stability?

Answer 35

The ability of a body to resist motion and to remain at rest.

Question 36

What are 4 factors that can affect stability?

Answer 36

Mass of the body
Height of centre of mass
Base of support
Line of gravity

Question 37

What is line of gravity?

Answer 37

An imaginary line which extends from the centre of mass downwards to the floor.

Question 38

How can mass affect stability?

Answer 38

The higher the mass, the greater the stability

Question 39

How can height of centre of mass affect stability?

Answer 39

The lower the centre of mass, the greater the stability.
If you are crouching down, your centre of mass is closer to the floor, so you are more stable. If you are standing on your tip toe, your centre of mass is higher so you are less stable.

Question 40

How can the base of support affect stability?

Answer 40

The wider the base of support, the greater the stability. If you have more points in contact with the floor, and they are wider apart, your stability will be better, e.g. on your hands and knees

Question 41

How can line of gravity affect stability?

Answer 41

If the line of gravity is central to the base of support, stability will be greater. If you are standing up straight, your line of gravity is central, between your legs so you are more stable, if you are leaning over your line of gravity isnt in the middle of your base of support so you are less stable.

Question 42

Give an example in sports where you would want to maximise stability.

Answer 42

A rugby player wants to maximise stability in a scrum so they are harder to be pushed over.

Question 43

Explain, using a sporting example, how an athlete can maximise stability.

Answer 43

To maximise stability a rugby player in a scrum will:
-Lower their centre of mass by crouching low to the ground
-Widen their base of support by having their legs apart
-Keep their hips over their ankles to keep their line of gravity central to their base of support.

Question 44

Give an example in sports when you would want to minimise stability

Answer 44

A sprinter wants to minimise their stability on ‘set’ so their falling forwards as they start, which minimises movement time so they can get a quicker start.

Question 45

Explain using a sporting example, how an athlete can minimise stability.

Answer 45

To minmise stability on ‘set’ a sprinter will:
-Lift their hips up to raise their centre of mass
-Raise one knee off the floor to reduce points of contact with the floor, therefore reducing the size of the base of support
-Move their shoulders forwards and hips forwards so they aren’t in line with their wrists and ankles, which moves their line of gravity forward from the centre of the base of support.