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Biomechanics > Week 4 > Flashcards

Week 4 Flashcards

1
Q

Define force

A

Any action which tends to cause a change in motion or shape of a body

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2
Q

Properties of a force (4)

A

Line of action (path of force)
Magnitude (N)
Direction (degrees or radius)
Point of application

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3
Q

How do you calculate applied force

A

Applied force = Force of vertical component + force of horizontal component

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4
Q

Newtons Laws of motion (3)

A

1st law - Law of Inertia
2nd law - Law of Acceleration
3rd law - Law of Reaction

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5
Q

Newtons 1st Law

A

Law of inertia - An object will remain at rest or in motion unless acted upon by a net external force

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6
Q

Newtons 2nd law

A

Law of acceleration - The change in motion of an object is proportional to the
force impressed; and is made in the direction of the
straight line in which it is impressed

F = ma
Force = mass x accelaration
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7
Q

Newtons 3rd law

A

Law of reaction - For every action there is an equal and opposite reaction

If object A exerts a force on object B, then object B exerts the same force on the object A but in the opposite direction

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8
Q

Name 5 types of forces

A 
Weight force
Muscle force
Ground reaction force (GRF)
Joint reaction force (JRF)
Friction
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9
Q

Difference between weight and mass

A

Mass is the amount of matter an object has calculated in kg

Weight is the force experienced by an object due to gravity measured in newtons

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10
Q

Calculation for weight

A

Mass x acceleration due to gravity (always 9.81m/s2) on earth

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11
Q

Weight of a 2kg dumbell

A

2kg x 9.81 m/s2 = 19.62 N

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12
Q

How much does someone weigh if their mass is 130kg?

A

130kg x 9.81m/s2

1275.3 N

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13
Q

Explain friction forces

A

Resistance to movement between two surfaces in contact measured in Newtons (N)

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14
Q

Explain what happens to velocity when friction is applied

A

Displacement will slowly decrease over time as friction will be acting against it, therefore velocity will decrease over time

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15
Q

Equation for friction

A

Ffriction = µ*FN

Ffriction – Frictional Force (Newtons) - force acting parallel to the
surface which opposes motion
µ - Friction Coefficient (dimensionless) - varies with surface
FN – Normal Force (Newtons) - force (component of GRF) acting
perpendicular to the surface

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16
Q

How can the coefficient of friction vary (μ)

A

The hardness and roughness of a surface

μ = 0 = perfectly smooth/frictionless

17
Q

What the difference be with a tyre on dry and wet road

A

Tyre on Dry Road µ ~ 1

Tyre on Wet Road µ = 0.2

18
Q

If we push rectangular object on a surface with 0.5 coefficient of friction and it moves 1 metre, how far would that same object be pushed if it was flipped on a side with a smaller surface area touching the ground?

A

1 metre. Friction is independent of surface area.

19
Q

If someone was sledding on a 200kg sleigh and the person on the sled was 75kg, what would the Normal Force be exerting against the sled?

A

275kg x 9.81m/s2

= 2697.75 N

In other words, it is exerting the exact same force back

20
Q

What is static friction

A

Frictional force required to overcome inertia

21
Q

What is dynamic friction

A

Kinetic or sliding friction

newtons 1st law

22
Q

Why do gymnasts apply chalk (magnesium carbonate) to their hands?

A

To reduce the friction from the bar to the hands

23
Q

What GRF does walking have on the body, measured in BW?

A

1-1.5 BW

24
Q

What GRF does running have on the body, measured in BW?

A

2-3 BW

25
Q

What GRF does jumping have on the body, measured in BW?

A

2-5+ BW

26
Q

Does landing on a slope skiing decrease the GRF and why?

A

Yes. The GRF is decreased as as the bodyweight is not landing flat, therefore the GRF is decreased depending on the angle of the slope. Steeper the angle, the lower the GRF.

27
Q

How much force does Doug have to push with to get the fridge to move?

Dougs force must be greated than the frictional force of the fridge. (Ffriction = µ*FN)

Fridge weighs 120kg. The µ is 0.5. How much force does he need to apply to move the fridge?

A

0.5 x (120kg x 9.81m/s2) = 588.6 N

Doug has to apply a force of <588.6 N to move the fridge

28
Q

Which brick has greater frictional force?

Brick A lying on the length side with a force of 29 N

OR

Brick B lying on the top side with a force of 29 N

A

Both will have the same amount of Ff as frictional force is independent of surface area

29
Q

Which brick has greater frictional force?

Brick C lying on the length side weighing 29 N

OR

Brick D lying on the length side weighing 87 N

A

Brick D will have greater frictional force as the weight of brick D is larger than Brick C as Ff = µ*FN

Biomechanics (20 decks)

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