Forces

Question 1

Define Newton’s First law - Law of Inertia

Inertia (definition)

NL1 Netball example

Answer 1

a body will remain at rest or constant velocity until an external force is applied

The resistance an object has to a change in its state of motion

Step 1 – stationary body will remain at rest until an external force is applied
The ball (body) will remain in the centres hands until she applies a force to the ball to pass it to a team mate

Step 2 - a moving object will continue to move with a constant velocity
The netball will continue to travel at a constant velocity in the direction thrown until caught by another player, where the balls velocity will decrease

Question 2

Define Newton’s Second Law - Law of Acceleration

What does it mean?

NL2 GS example

Answer 2

The rate and change of momentum is directly proportional to the force acting upon it and in the direction in which it is applied

It means the size (magnitude) and direction of the force applied to the body determines the magnitude and direction of the acceleration given to the body

When GS receives the ball close to the post, she will only need to impart a small amount of force

If the GS receives the ball at the edge of the circle, she will need a larger force in the direction of the post as it will need a greater change of momentum to travel

Question 3

Define Newton’s Third law - Law of Reaction

What it means?

NL3 Ball and player example

Answer 3

To every action there is an equal and opposite reaction

This describes what happens when two bodies exert force on one another
Key forces act in pairs

2 types of forces:

         - Action Force – generated by the body to the ground or an object
         - Reaction Force – is the equal and opposite force generated by the ground/object OR object back to the body

Example

• Player exerts an action force on the ball in a downward direction
• Ball exerts a reaction force in the upward direction on the player
• Ball then travels to the floor where it becomes the action force (downwards onto the ground.
• The ground exerts an upward reaction force on the ball and the ball bounces upwards

Question 4

Apply Newton’s Laws of motion to explain how a basketball player would jump up to block a shot (6)

Answer 4

NL1

• a body continues in a state of rest or uniform velocity unless acted upon by and external force (AO1)
• To leave the ground the player must exert a greater force into the ground than their weight (AO2)

NL2

• when a force acts on an object, the rate of change of momentum is directly proportional to the force applied and takes place in the direction in which it is applied
• The basketball player accelerates upwards – the greater the force the greater acceleration/higher the jump

NL3

• for every action there is an equal and opposite reaction (AO1)
• The player pushes downwards on the ground and the ground applies an equal and opposite force upwards on the player (AO2)

Question 5

Velocity

Definition
Calculated By
Measured In

Answer 5

Rate of change in displacement (shortest straight-line route between start and finish point)

velocity = displacement/time taken

metres per second (m/s)

Question 6

Momentum

Definition
Calculated By
Measured In

Answer 6

Quantity of motion possessed by a moving body

momentum = mass x velocity

kgm/s

Question 7

Acceleration

Definition
Calculated By
Measured In

Answer 7

Is the rate of change in velocity (usually use a split time)

acceleration = (final velocity - initial velocity) / time taken

metres per second squared (m/s2)

Question 8

Force

Definition
Calculated By
Measured In

Answer 8

A push or pull that alters the state of motion of a body

force = mass x acceleration

Newtons (N)

Question 9

Two Types of Force (definition and example)

Answer 9

Internal Forces:

        - Generated by the contraction of the muscle
        - For example: Usain Bolt contracts his rectus femoris to extend his knee. The gastrocnemius to plantarflex the ankle. Both of which will assist him to leave the blocks

External Forces:

        - From outside of the body and acts upon it. 
        - These forces include: weight, reaction, friction and air resistance

Question 10

What are the 5 effects of force?

Use football as an example for each

Answer 10

• create motion
  the football will remain at rest on the penalty spot until a force is applied to it
• accelerate a body
  the greater the force applied by the footballer’s foot to the ball, the greater the rate of acceleration towards the goal
• decelerate a body
  as the ball moves through the air towards the goal, the force of air resistance will act in the opposite direction and slow it down
• changing the direction of a body
  as the goalkeeper dives to save a high corner shot, he will apply force from his hands to the ball, changing it’s direction pushing it away from the goal
• changing the shape of a body
  if the goalkeeper fails to make the save, the force of the ball coming into contact with the net will change the shape of the net.

Question 11

What is net force?

If net force = 0 there is no change in motion as the forces are ___________. This means that body will remain at _____ or travel with ___________ ____________.

What are Balanced Forces?

What are Unbalanced Forces?

If a net force exists there will be a change in motion as the forces are unbalanced. This imbalance is what causes the body to: (4)

Answer 11

Sum of all forces acting on a body (aka resultant force). It is the overall force acting on a body when all individual forces have been considered

When we consider all forces we can see the overall motion of the body.
If net force = 0 there is no change in motion as the forces are balanced. This means that body will remain rest or travel with constant velocity.

two or more forces action on a body are equal in size and opposite in direction

two or more forces unequal in size and opposite in direction = net force

• Accelerate
• Decelerate
• Change direction
• Change shape

Question 12

Net Force - Basketball Example (3)

Net Force - Badminton Example (2)

Answer 12

Basketball

• In the chest pass forwards force is > than the air resistance OR gravitational pull.
• Meaning it accelerates directly to the chest of team mate.
• Leads to positive net force

Badminton

• Shuttle cock decelerates rapidly due to air resistance acting in the opposite direction
• Leads to a negative net force

Question 13

What are the 2 vertical forces?

What are the 2 horizontal forces?

Answer 13

Vertical:

• weight
• reaction

Horizontal:

• air resistance
• friction

Question 14

Weight

What is it?
What is it measured in?
When is it present?
Where does it act?
Where is it on diagrams?
How is it calculated?

Answer 14

• This is the gravitational pull that the earth exerts on a body
• Measured in Newtons (N)
• This force is always present
• Acts downwards from the body’s centre of mass
• On diagrams it is a vertical arrow pointing downwards
• Calculated by: weight = mass X acceleration

Question 15

Reaction

What is it?
What is measured in?
What is a result of?
When is it present?
How is it showed on a diagram?

Answer 15

• Equal and opposite force exerted by a response to the action force (weight force)
• Measured in Newtons (N)
• Result of Newtons third law of reaction
• Always present when two bodies are in contact
• Normal reaction can be shown by a vertical arrow pointing upwards (from point of surface)

Question 16

Girl doing handstand forces acting diagram

Answer 16

Question 17

Factors affecting friction

How does it affect friction and give an example for each one

Answer 17

Roughness of ground surface

• increasing roughness = increased friction
• For example: athletes run on rough rubberised tracks

Roughness of contact surface

• increasing roughness = increasing friction
• For example: athletes such as sprinters, jumpers wear shoes with spikes

Temperature

• increasing temperature = increasing friction
• e.g. F1 drivers have warm up lap

Size of normal reaction

• increasing normal reaction = increasing friction
• e.g. shot-putters have high mass - equal / opposite high reaction force - greater friction - prevents over-rotation

Question 18

Factors affecting Air Resistance

How does it affect air resistance and give an example for each one

Answer 18

Velocity

• increasing velocity = increasing air resistance
• For example: > the velocity of a sprint cyclist the > the force of air resistance opposing their motion

Shape

• increased aerodynamic = decreasing air resistance
• For example the shape of the sprint cyclists helmet. Known as streamlining – creation of smooth air flow around an aerodynamic shape

Frontal cross-sectional area

• decreasing frontal cross-sectional area = decreasing air resistance
• For example: the low crouched position of giant slalom skiers in the straight section

Smoothness of surface

• increasing smoothness = decreasing air resistance
• For example: smooth lycra suits of sprinters, skiers etc

Question 19

Streamlining (definition)

Answer 19

creation of SMOOTH AIR FLOW around an AERODYNAMIC shape to minimise air resistance

Question 20

Centre of mass (definition)

Stability (definition)

Sometimes being unstable is an advantage (3 reasons why)

Answer 20

• The point at which a body is balanced in all directions; the point at which weight appears to act
• The ability of a body to resist motion and remain at rest

1. Because you want to change direction
2. You need to rotate
3. You want to increase the range of motion or stretch

Question 21

Factors affecting stability

How does it affect air resistance and give an example for each one

Answer 21

Mass of the body:

       - the greater the mass of a body the greater its inertia therefore the greater the stability
       - For example sumo wrestlers, rugby props have a high mass and can withstand great applied forces

Height of the centre of mass:

         - the lower the centre of mass, the greater the stability
         - For example when a gymnast lands a jump they have flexion at the knee and hip to lower the COM to create a stable landing

Base of support:

        - the greater the size of the base of support, the greater the stability
       - Simple way to widen the stance  of your two feet or increase the number of contact points on the ground
       - For example Table tennis players stands with feet wider that shoulders to increase their stability

Line of gravity - the line imaginary line that extends from the COM down to the foot:

        - More central the line of gravity to base of support the greater the stability
        - For example netball GS line of gravity falls within base of support making them stable. The GK line of gravity falls outside and in front of base of support making them less stable