Lectures 5-11

Question 1

What does a force do? And what does a force have?

Answer 1

It acts on an object to cause or resist a motion

Forces have a magnitude and a direction

Question 2

What is Newton’s first law? What is the fancy name for it?

Answer 2

A body continues in a state of rest or uniform velocity unless acted upon by an external or unbalanced force

Law of inertia

Question 3

What is Newton’s second law of motion? What is the fancy name for it?

Answer 3

A body’s rate of change of momentum is proportional to the size of the force applied and acts in the same direction as the force applied

Law of acceleration

Question 4

What is the equation for force?

Answer 4

Force = mass x acceleration

1N = 1kg x 1m/s/s

Question 5

Definition of weight

Answer 5

The gravitational pull that the earth exerts on a body

Question 6

What is the equation for weight

Answer 6

Weight (N) = Mass (kg) x Acceleration due to gravity

W=mg

Question 7

Definition of momentum

Answer 7

The quantity of motion that an object has

Question 8

Equation for momentum?

Answer 8

Momentum = Mass x Velocity

Question 9

Conservation of momentum (Check this, slide 14, lecture 5)

Answer 9

The momentum before will equal the momentum after unless the object is acted upon by an external force

Question 10

Look at question, slide 18, lecture 5

Answer 10

Important question this

Question 11

Look at lecture 5, slide 19

Answer 11

For the link between force & velocity

Question 12

What is Newton’s third law of motion? What is the fancy name for it?

Answer 12

For every action there is an equal and opposite reaction

Law of reaction

Question 13

Look at pages 86 + 87 in PE book

Answer 13

For free body diagrams

Question 14

Definition of friction

Answer 14

A force that opposes the motion of two surfaces in contact

Look at slide 13 lecture 6 definition, bit weird though

Question 15

Equation for the coefficient of friction

Answer 15

Coefficient of friction = frictional Force / normal force

Look at slide 16, lecture 6 for the symbols

Question 16

Recap example

Answer 16

Lecture 6, slide 17

Question 17

Recap

Answer 17

Lecture 6, slide 17-20

Question 18

Definition of stress

Answer 18

Stress is the force distributed over a given area

Question 19

Equation for stress? What is stress measured in?

Answer 19

Stress (Pa) = Force (N) / Area (metres squared)

Stress is measured in pascals

Look at slide 4, lecture 7 for symbols

Question 20

Definition of strain?

Answer 20

Strain is the deformation of a tissue

Question 21

Equation of strain?

Answer 21

Strain = change in length (m) / original length (m)

Strain = deformation / original shape

Question 22

What are the units for strain? (Check this on recap/google, slide 5, lecture 7)

Answer 22

Unitless / %

Question 23

Look at the stress ~ strain relationship slide 6, lecture 7

Answer 23

Recap it as well

Question 24

Recap

Answer 24

Slide 8 - 21, lecture 7

Question 25

Definition of centre of mass

Answer 25

The point at which an object or a body is balanced in all directions, the point at which weight appears to act

Question 26

Definition of (static) equilibrium

Answer 26

A state where net force acting on an object is zero

Question 27

Definition of stability

Answer 27

Stability is the ability of an object to resist a disruption to equilibrium and to return to its normal state

Question 28

Tests of balance

Answer 28

Timed single leg stand Functional reach test

Question 29

Definition of centre of pressure (CoP)

Answer 29

The point where force acts across an area

Question 30

Recap

Answer 30

Slide 7, lecture 9

Question 31

Equation for Work

Answer 31

Work (joules) = Force x Displacement

Question 32

Units of Work

Answer 32

Joules

Question 33

What are the directions of Work?

Answer 33

Positive Negative Isometric contractions

Question 34

In terms of directions of Work, what does positive Work mean? What type of muscular contraction is positive Work?

Answer 34

Force and displacement in the same direction Concentric contraction

Question 35

In terms of direction of Work, what does negative Work mean? What type of muscular contraction is negative Work?

Answer 35

Force and displacement in the opposite direction Eccentric contraction

Question 36

In terms of direction of work, what type of Work is an isometric contraction?

Answer 36

No mechanical Work

Question 37

Equation for potential energy

Answer 37

Potential energy (Joules) = Mass x Gravity x Height

Question 38

Equation for potential strain energy

Answer 38

Potential strain energy (Joules) = 1/2 proportionality constant x distance deformed squared

Question 39

What are the units for Potential Strain Energy?

Answer 39

Joules

Question 40

Equation for Kinetic Energy

Answer 40

Kinetic Energy (Joules) = 1/2 Mass x Velocity squared

Question 41

What are the units for kinetic energy?

Answer 41

Joules

Question 42

What is the conservation of energy?

Answer 42

Energy can neither be created nor destroyed, it can only be changed from one form to another

Question 43

What is the equation for Total Energy?

Answer 43

Total energy = Kinetic energy + Potential energy

Question 44

Equation for power

Answer 44

Power (Watts) = Force x Velocity

Question 45

What is the unit of Power?

Answer 45

Watt

Question 46

What are the different methods that can be used to calculate power? What is the choice of method very dependent upon?

Answer 46

Linear position transducer Kinetic Kinematic ~ Kinetic methods The choice of method is very dependent upon the context

Question 47

Recap slide 9, lecture 9

Answer 47

Weird

Question 48

Equation for impulse

Answer 48

Impulse = Force x Time Or Impulse = Ft = /_\M = m(v2-v1) = m/_\v

Question 49

Equation for momentum?

Answer 49

Momentum = Mass x Velocity

Question 50

What are the applications for impulse?

Answer 50

Measure final velocity Predict how much force you’ll need How long do you need to apply a force for How much less force is needed if I reduce mass

Question 51

Example questions

Answer 51

Slide 8 + 10 | Lecture 10

Question 52

In terms of Impact, what is deformation?

Answer 52

Deformation occurs when impact occurs, for example the tennis/golf ball example, where it moves when hit

Question 53

In terms of restitution, what is deformation?

Answer 53

After deformation has occurred and it has returned to its normal shape

Question 54

Recap inelastic and elastic stuff

Answer 54

Slide 13, lecture 10

Question 55

Equation for coefficient of restitution

Answer 55

Coefficient of restitution (e) = square root of (bounce height/drop height)

Question 56

What is the centre of percussion?

Answer 56

The point about which a force can be applied without causing an acceleration at the centre of rotation

Question 57

What are the phases on the stress strain graph?

Answer 57

Elastic -> yield point -> plastic

Question 58

What does the elastic phase mean of the stress strain graph?

Answer 58

It is where the object is deformed but it will still return to its original shape

Question 59

What is the yield point on the stress strain graph?

Answer 59

This is the point where if stress/strain continues past this point the object will deform and not return to its original shape

Question 60

What is the plastic phase on the stress strain graph?

Answer 60

It is the point where the object has become so deformed it will not return to its original shape

Question 61

Definitions of stress and strain

Answer 61

Strain - is the relative change in shape or size of an object due to externally-applied forces Stress - is the internal force (per unit area, etc) associated with a strain

Question 62

What does more stress result in?

Answer 62

More deformation

Question 63

Factors affecting stability

Answer 63

Mass Height of centre of mass Size of the base of support Line of gravity

Question 64

How does the functional reach test work?

Answer 64

Get someone to reach out as far as they can before they feel they are going to fall over

Question 65

Factors affecting balance

Answer 65

Posture Vision Environment Muscle strength

Question 66

What is Force proportional too?

Answer 66

Force is proportional to change in momentum over change in time

Question 67

How do Force and velocity link?

Answer 67

Write it out, remember from slide 19, lecture 5 Hint: what is the equation for force?

Question 68

What is a coefficient of friction value between?

Answer 68

0-1 | Except in certain cases

Question 69

On the coefficient of friction graph what are the stages?

Answer 69

Static then Kinetic