Biomechanics- Principles Flashcards
Define Newtons three laws of linear motion
- … a body will remain in a state of rest or uniform motion until a force acts upon it.
- acceleration is directly proportionate to the magnitude of the force produced and is governed by the direction the force is applied/
[force= mass x acceleration] - Law of Action/Reaction - for every action there is an equal and opposite reaction.
During the race, a swimmer has to dive off the starting blocks as quickly as possible.
Using ‘Newton’s First and Second Laws of Motion’, explain how the swimmer dives off the starting blocks.
(Total 4 marks)
**Newton’s First Law of Motion / Law of inertia**
Performer will remain on the blocks unless a force is applied.
Do not credit push.
Performer continues to move forwards with constant velocity until another force is applied.
Law has to be identified to be credited marks.
Water slows the swimmer.
Newton’s Second Law of Motion / Law of Acceleration
Mass of swimmer is constant.
Stating the law no marks but must be applied to the swimmer.
Greater the force exerted on the blocks, the greater the acceleration / momentumForce governs direction.
Don’t accept velocity.
Not F=ma.
The final stage of an endurance race often involves a sprint finish.
Using Newton’s Second Law of Motion, explain how an athlete is able to accelerate towards the finish line.
(Total 3 marks)
Mass of runner is constant.
Force = Mass x Acceleration.
Not f = ma – full terms only.
Greater the force exerted on the floor, the greater the acceleration / momentum / proportional.Force governs direction.Force provided by muscular contraction.
Do not accept ‘legs’.
Ground reaction force.
must be in context / not GRF.
During physical activity, sport performers exert large forces, which may cause injury.
Identify one vertical force and one horizontal force acting on a performer when running in a 100 metre sprint.
(Total 2 mark)
Vertical – weight / reaction force / gravity
ANDHorizontal – friction / air resistance
Requires both responses for one mark
Do not accept wind resistance
Analyse, using Newton’s First and Second Laws of motion, how a footballer will move towards the ball from a stationary position.
(Total 4 marks)
First Law
* The footballer will provide force by contracting his leg muscles (1) using this force he can overcome inertia, allowing him to move from a stationary position (1)
Second Law
* By varying the force of his muscles’ contraction/the number of motor units recruited the footballer can cause a change in momentum from stationary to moving (1) therefore the greater the force he generates the greater the acceleration to the ball (1)
Accept other appropriate responses using Newton’s First and Second Laws of motion to analyse how a footballer will move towards a ball.
Max 4 marks
It is important for sprinters to push off the blocks effectively to achieve a fast start.
Using Newton’s first and second laws of linear motion and knowledge of the neuromuscular system, analyse how a sprinter is able to achieve a fast start.
(Total 8 marks)
AO1 – Knowledge of Newton’s first and second laws of linear motion and the neuromuscular system
Newton’s first and second laws – Eg First law is the law of inertia. Inertia is a body’s reluctance to change its state of motion. A force is required to overcome inertia. Second law is the law of acceleration, the rate of change of momentum of an object is directly proportional to the force causing the change. Any change in momentum takes place in the direction the force was applied.
Force = mass × acceleration
Neuromuscular system – Eg three muscle fibre types, type I, type Ia, type IIx. Muscle contraction brought about by the recruitment of muscle fibres. Spatial summation is when the strength of a contraction changes by altering the number of size of motor units. Wave summation is where there is a repeated nerve impulse with no time to relax so a smooth, sustained contraction occurs. This is a tetanic contraction. Muscle fibres form a motor unit (with motor nerve), each muscle fibre in the unit contracting or relaxing at the same time. This is according to the all-or-none law. There are different sizes of motor unit.
**
AO2 – Application of Newton’s first and second law and the neuromuscular system to a sprinter**
Eg The sprinters current state of inertia is stationary; to alter this state of inertia the sprinter needs to apply a muscular force by contracting his leg muscles in order to overcome his inertia so that he can leave the blocks, moving from a stationary position to begin to run.
By varying the force of his muscles’ contraction and the number of motor units recruited the sprinter can cause a change in momentum from stationary to moving. The sprinter applies a force against the blocks and then the ground to generate the required momentum to move forward down the track.
It would be beneficial to the sprinter to have a high percentage of fast twitch fibres type IIx. The sprinter will recruit large, fast twitch motor units in the leg muscles to generate the force required to overcome inertia, the sprinter will use spatial summation, varying the number of motor units recruited throughout the muscle to allow the fibres in each unit to relax whilst others are contracting to provide the necessary force.
AO3 – Analysis / Evaluation of how the sprinter is able to achieve a fast start
Eg The greater the muscular force that the sprinter can apply against the blocks, the more readily the body will alter its state of inertia, allowing the sprinter to move more quickly out of the blocks. By varying the force of his muscles’ contraction, the greater the force he generates, the greater the acceleration away from the blocks, giving him a better start than his competitors.
If the sprinter increases the frequency of stimulation of the muscle fibres in the motor unit such that the next impulse reaches the muscle before it has completely relaxed from the previous the resulting force is greater, hence the sprinter may use wave summation to increase the force of the muscle contraction further, generating a greater force and therefore greater acceleration according to Newton’s second law.
Accept other appropriate analysis of Newton’s first and second laws of linear motion and the neuromuscular system in enabling a sprinter to achieve a fast start.
How would you calculate
- Distance
- Speed
Distance= Speed x Time
Speed= Distance divided by time
Calculate the following equations
1.5k swim timed at 30 mins and 30 secs- Average speed (M/S)=
40k cycle timed at 90 mins- average speed (M/S)=
10km run timed at 45 mins- average speed (M/S)=
1= 0.82 m/s
2= 7.41 m/s
3= 3.7 m/s
Which one of the following is the definition of mass
A= The amount of space a body occupies
B= The gravitational force exerted on an object
C= The quantity of matter a body possesses
C
A runner completes 400m at an average speed of 5 m/s.
How long does it take the runner to complete 400m?
[total 1 mark]
1 minute and 20 seconds
Whichoneof these measurements is a scalar quantity?
A= Displacement
B= Mass
C= Velocity
D= Weight
B
What is the average speed of a performer who runs 200 metres in 20 seconds?
(Total 2 marks)
- 200 ÷ 20 = 20
- m/s or ms-1
Below is a distance time graph for a cycle sprint.
Using the graph, calculate the speed of the cyclist between 40 and 70 seconds. [total 2 marks]
Awardonemark for each of the following points.
AO2
* 300m/30s (1)
AO3
* 10m/s / m.s–1/ metres per second (must show units) (1)
Accept other appropriate statements demonstrating improvement in health or performance.
Define and explain the concept of centre of mass in relation to forces.
[total 3 marks]
Awardonemark for each of the following points (max 3 marks):
* CoM - unique point of object where its weight can be considered to act
* Object of uniform shape and density - CoM = centre of shape
* Force applied through CoM / concentric force - body moves in straight line / linear motion
* Force not applied through the centre of mass / eccentric force - rotation / angular motion produced
The diagram below shows a gymnast holding a headstand.
Statetwofactors that affect the stability of a gymnast holding a headstand.
(Total 2 marks)
Awardonemark for each of the following points.
* Height of centre of mass of the gymnast (1).
* Area of base of support for the headstand (1).
* Position of line of gravity and body mass (1).
Accept any other relevant factors that affect the stability of a gymnast holding a headstand.
The picture below shows a rugby player about to make a tackle.
Analyse how factors affecting stability can affect the success of a rugby player’s tackle.
(Total 8 marks)
AO1 – Knowledge of factors affecting stability.
* Centre of mass (COM), height of COM, width of base of support, mass of performer, line of gravity and friction.
* Description of how factors impact stability in general terms e.g. Mass of player- greater the mass the more stable. Base of support - the wider the base of support, the more stable.
AO2 – Application of factors affecting stability to a rugby player making the tackle.
* Line of gravity – the tackler will try and have this aiming through middle of the base of support to increase stability.
* The tackler’s line of gravity is positioned in the middle of the base of support.
* The tackler has created a wide base of support by increasing the width of their feet which will increase stability.
* The tackler has both feet in contact with the ground, rather than one leg, which increases contact points and stability.
* The tackler has lowered their centre of mass by flexing / bending the knees.
* The tackler’s mass is large which increases stability. Accept reverse for player with ball
* The tackler’s footwear / boots will support an increase in friction by the studs gripping in the ground.
* If the tackler has poor footwear / boots or the ground is wet / slippery they may not gain a lot of friction and this could affect their movement into the tackle.
AO3 – Analyse how the factors affecting stability can affect the success of the tackle.
* Too much mass may make the player less stable, however may affect the dynamics / mobility / loss of stability when making the tackle.
* There will be an optimal width for the base of support, too wide and the tackler will lose dynamics / ability to change direction quickly, too narrow and the player compromises stability and effectiveness of the tackle.
* The tackler may shift this line of gravity closer to the edge of the base of support, to enhance a change in direction for the tackle.
* Altering height of COM could enable the player to tackle more effectively, by lowering tackling legs / hips to take player down or moving higher to regain possession of the ball.
Accept any other appropriate analysis of how factors affecting stability can influence / affect the rugby player making a tackle.
Explain how a performer can best maintain stability.
(Total 8 marks)
AO1- Identify factors affecting stability
Award up totwomarks for:
* Stability is the ability to maintain balance/equilibrium.
* Factor - Height of centre of mass.
* Factor - Area of base of support.
* Factor - Line of centre of gravity.
* Factor - if performer is moving, mass affects stability.
AO2- Application to situation
Award up tothreemarks for:
* Factor - Height of centre of mass, ie lower centre of mass means more stability.
* Factor - Area of base of support, ie a wider base of support means more stability.
* Factor - Line of centre of gravity, ie closer to the base of support means more stability.
* Factor - if performer is moving, mass affects stability, ie the greater a performer’s mass the greater their stability.
AO3- Analyse situation
Award up tothreemarks for:
The base of support is the area beneath an object or person that includes every point of contact that the performer makes with the ground. The greater the base of support the more stable. The base of support for most performers is the area between their feet and so getting their feet wide apart will increase their base of support to become more stable. In some activities/situations, performers may be able to play one or both hands on the floor. This will increase their base of support and make them more stable, e.g.gymnast and headstands, three point stance in rugby. If a performer reduces the height of their centre of mass and gets it closer to their base of support by squatting down, this will also make them more stable, e.g.in martial arts. Making sure that their line of gravity stays within their base of support will also make them more stable.
