Biomechanical Principles - Newtons Laws, Forces, Free body diagrams, Stability Flashcards
What are Newton’s 3 laws of motion?
1 - Law of inertia
2 - Law of acceleration
3 - Law of reaction
Describe Newtons 1st Law
The law of inertia states that a body will remain at rest of constant speed unless acted upon by an external or unbalanced force.
Describe Newtons 2nd Law
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)
Describe Newtons 3rd Law
Newtons law of reaction states that for every reaction there is an equal and opposite reaction.
Give a sporting example of Newtons 1st Law
A football won’t move unless it is moved by an external force ( a foot kicking it)
Give a sporting example of Newtons 2nd Law
The bigger the force applied to a sprinter when they start moving, the faster they will accelerate from the blocks.
Give a sporting example of Newtons 3rd Law
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.
What is a force?
A push or pull that alter the state of motion in a body.
How do you calculate force?
Force = mass x acceleration
What is force measured in?
Newtons ( N )
What does the term net force mean?
The sum of all forces acting on the body/ the overall force acting on the body when all forces have been considered.
What is meant by the term ‘balanced force’?
A balanced force occurs when 2 or more forces acting on a body are equal in size and opposite in direction.
What is meant by the term ‘unbalanced force’?
An unbalanced force occurs when two forces are unequal in size and opposite in direction.
On a free body diagram, what are the two vertical forces?
Weight - Downwards
Reaction - Upwards
On a free body diagram, what are the two horizontal forces?
Friction ( forwards )
Air Resistance ( backwards)
What is weight?
The gravitational pull that the earth exerts on a body.
What is reaction?
The equal and opposite force exerted by a body in response to the action forces places upon it.
What is friction?
The force that opposes the motion of two surfaces in contact.
What is air resistance?
The force that opposes the motion of a body travelling through the air.
Where do you draw the weight arrow from on a free body diagram?
The centre of mass downwards
Where do you draw the reaction arrow from on a free body diagram?
The points in contact with the floor going upwards
Where do you draw the friction arrow from on a free body diagram?
The points in contact with the floor going forwards
Where do you draw the air resistance arrows from on a free body diagram?
The centre of mass, backwards
What does it mean if the weight arrow is bigger than the reaction arrow
Weight is bigger than reaction, therefore you are moving downwards / squatting
What does it mean if the reaction arrow is bigger than the weight arrow?
Reaction is bigger than weight, therefore you are moving upwards ( but still in contact with the floor) - taking off for a jump
What does it mean if the friction arrow is bigger than the air resistance arrow?
You are accelerating
What does it mean if the air resistance arrow is bigger than the friction arrow?
You are decelerating
What does R>W mean?
Give a sporting example to show when it might occur.
Reaction is bigger than weight.
A basketball player is moving upwards during the take off for a slam dunk
What does R<W mean?
Give a sporting example to show when it might occur.
Reaction is less than weight.
A weight lifter is moving downwards in a squat.
What does F>AR mean?
Give a sporting example to show when it might occur.
Friction is less than air resistance.
A sprinter is accelerating off the blocks
What does F<AR mean?
Give a sporting example to show when it might occur.
Friction is less than air resistance.
A sprinter slowing down age crossing the finish line
What does R=W mean?
Give a sporting example to show when it might occur.
Reaction is equal to weight.
There is no vertical movement to an action, e.g. a 1500m runner is moving forwards
What does F=AR mean?
Give a sporting example to show when it might occur.
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)
Describe the term ‘centre of mass’
The point at which a body is balanced in all directions.
What is stability?
The ability of a body to resist motion and to remain at rest.
What are 4 factors that can affect stability?
Mass of the body
Height of centre of mass
Base of support
Line of gravity
What is line of gravity?
An imaginary line which extends from the centre of mass downwards to the floor.
How can mass affect stability?
The higher the mass, the greater the stability
How can height of centre of mass affect stability?
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.
How can the base of support affect stability?
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
How can line of gravity affect stability?
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.
Give an example in sports where you would want to maximise stability.
A rugby player wants to maximise stability in a scrum so they are harder to be pushed over.
Explain, using a sporting example, how an athlete can maximise stability.
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.
Give an example in sports when you would want to minimise stability
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.
Explain using a sporting example, how an athlete can minimise stability.
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.
