Week 1: Intro to Biomechanics

Question 1

Define biomechanics (3 points)

Answer 1

• Bio = living
• Mechanics = study of action of forces
• Biomechanics = the study of forces and their effect on living systems

Question 2

Describe sports and exercise biomechanics

Answer 2

Study how forces effect and relate to exercise, movement or various sports

Question 3

Describe the two branches of biomechanics (7 points)

Answer 3

• Kinetics = forces that cause or tend to cause motion
  
  • Cause the change in motion, but are not visible to the observer
  • Example: force, power, impulse
  • Further broken into two subdivision: internal (i.e. muscles) and external (i.e. gravity)
• Kinematics = description of motion
  
  • Kinematic variables are always visible
  • Example: displacement (how far something is moved), velocity (how far something is traveling)

Question 4

Identify the goals of sports and exercise biomechanics (7 points)

Answer 4

• The primary goal is to improve performance, however this can be broken down into different sub categories such as:
  
  • Injury prevention: to make sports safer for participants
    
    • Rehabilitation: if an injury does occur, biomechanics can be used to build a rehab program
  • Develop and enhance sports techniques: improve an athletes performance and potentially decrease their injury risk
  • Develop better sports equipment: improve performance and decrease injury risk
  • Training improvement
• Each subcategory interrelates to one another

Question 5

Define force

Answer 5

A push or pull that alters or has the tendency to alter a body’s motion

Question 6

Explain measurement of force and formula to determine force (4 points)

Answer 6

• Measured in Newtons (N)
• 1 Newton of force will accelerate a 1 kg mass at 1 m/s/s
• Rate of acceleration = m/s/s = m/s2 = ms-2
• Force = mass x acceleration

Question 7

Name and describe the characters of force (4 points)

Answer 7

• Magnitude: the strength of the force, how big or small it is
• Direction: where the force is getting applied
• Point of application: the exact location that the force is being applied to
• Line of application: the direction the force is being pushed through in terms of where it is being pushed on the point of application

Question 8

Describe the two types of physical quantities (6 points)

Answer 8

1. Scalar
   - Magnitude only
   - Example: speed, distance, mass, time
2. Vector
   - Magnitude and direction
   - Example: velocity, displacement, force, acceleration

Question 9

Name and define the classifications of forces (2 points)

Answer 9

• Internal forces: forces that act within the object or system whose motion is being investigated
• External forces: force that acts on an object

Question 10

Name and describe the types of internal forces (4points)

Answer 10

1. Tensile- internal pulling forces in opposite direction (tension)
2. Compressive- internal pushing (squeezing) force acting on the ends of internal structures (compression)

• Internal forces do not accelerate the body as the two forces are applied in opposite direction. However, they do help to maintain structure and integrity
• If the forces are too large, the structure may fail or break.

Question 11

Name and describe the types of external forces (6 points)

Answer 11

1. Contact
   - Occur with two objects that are in contact
   - Reaction forces with another body or fluid (air/water resistance)
2. Non-contact
   - Occur even though there is no contact between objects
   - Example: Gravity, magnitude

Question 12

Define gravity

Answer 12

A force of nature that works between two bodies of matter in the universe and tries to pull them together

Question 13

Describe gravity (5 points)

Answer 13

• Gravity is a vertical force, meaning it pulls objects to the center of the earth. It does not effect horizontal motion and will only change the vertical motion of an object.
• The distance an object is from the centre of the earth will have an influence on the gravitational effect. Meaning when an object is at a greater distance from the centre of the earth, gravity’s effect on the object decreases.
• For example, the distance a the Poles to earths center is less, therefore the effect of gravity is greater at 9.82 ms-2 compared to the gravitational effect at the equator at 9.78 ms-2.
• In addition, the gravitational effect will also be less in high altitudes since the location is further away from the earth’s core
• Gravity has large implication for projectile motion in sport. Although it can vary slightly, the average acceleration caused by gravity is 9.81 ms-2

Question 14

Define mass

Answer 14

The amount of matter in an object. It is a scalar quantity and is measured in kg

Question 15

Define weight

Answer 15

The force of gravity acting on an object. It is a vector and measured in newtons. Weight = mass x effect of gravity (standing stationary = 9.81)

Question 16

What is the difference between weight and mass?

Answer 16

With movement, a persons mass does not change. However, the weight of the person may change.

Question 17

Describe contact forces (7 points)

Answer 17

• A force that occurs between objects hat are in contact
• Can be a solid objects or fluids
• In sports, these are mostly contacts between solid objects
• Three categories of contact forces:
  
  • Ground Reaction Force (GRF): Equal and opposite force
  • Normal force: perpendicular to a surface
  • Frictional force: parallel to a surface

Question 18

Describe Ground reaction force (2 points)

Answer 18

• Ground reaction force (GRF) = An equally and oppositely directed force from the earth or different object.
• For example, to jump in the air, you must be in contact with the ground and push down on it. The GRF then acts from the ground equally and in opposite direction and accelerates you into the air.

Question 19

Describe normal force (5 points)

Answer 19

• Also known as normal contact force or normal reaction force.
• Force acting perpendicular to two surfaces in contact
• It’s magnitude can intentionally be altered to maximise friction.
• For example, adding more weight to a sled will act down in a perpendicular direction. This maximizes the normal force to make moving the sled more difficult
• Normal reaction forces (R) will always act perpendicular (right angles) to the surface of contact

Question 20

Describe friction (10 points)

Answer 20

• Two kinds of friction
  
  • Static friction: limiting friction
  • Dynamic friction: sliding friction
• Friction is proportionate to the normal force
• Affected by types of materials in contact
• Greater friction between softer, rougher surfaces than
  harder, smoother ones
• Not affected by surface area!!!
• Formula: friction force = uR
  
  • u is the coefficient of friction. This is what is affected by material types
  • R is the normal force

Question 21

Name sport examples of modifying the coefficient of friction and normal force

Answer 21

• Sport examples of modifying u:
  
  • Gloves in golf increases u between the glove and golf club so that club is less likely to slip out of hand and affect the shot
  • Table tennis bat increase u between the bat and ball, which allows the handler to apply more spin to the ball, causing the ball to curve and change its trajectory
  • Wax on snowboards decreases u between the board and snow, allowing faster movement when the board is in contact with snow
• Sport examples of modifying R:
  
  • Spoilers on cars takes air and pushes it up, giving an opposite and equal reaction and push the car back down to the ground. This will increase the weight of the car, thus increasing the R which in turn increases the friction. This provides the driver better control of the car.
  • Brake pads in cars and bikes will act in a perpendicular direction to the tire’s traveling motion, creating an normal reaction force which in turn creates friction. This will slow the bike or car down.
  • Weighted or unweighted ski

Question 22

Describe rolling friction (5 points)

Answer 22

• A force opposing the motion of an object as it rolls
  across another surface
• Increase deformation of surfaces = increased rolling
  friction
• Examples:
  
  • Hard, short grass on golf green will allow the ball to roll, however if the green is too hard and/or short it will be too difficult to stop the ball when putting
  • Sand vs Concrete: sand is going to a greater amount of friction that concrete
  • Tread thickness: a thicker tread in a bike tire has a greater rolling friction

Question 23

Describe collinear forces (4 points)

Answer 23

• Forces that have the same line of action
• May act in the same or different directions. As long as the have the same line of action, they would be considered collinear forces
• The forces can be added to calculate the total force
• Example: tug of war

Question 24

Describe concurrent forces (2 points)

Answer 24

• Forces that do not act along same line, but do act through the same point
• Example: gymnast hanging from high bar and coach applies force to front and back of torso to stop swing. These forces are acting at the same point (the gymnasts torso) but not along the same line (the the body weight force of the gymnast is moving down and the two forces of the coach is moving east and west)

Question 25

Define Resolution Forces

Answer 25

Forces that have a vertical and horizontal component

Question 26

Describe free body diagrams (5 points)

Answer 26

• Sketch that shows a defined system in isolation with all the force vectors acting on the system
• defined system: the body of interest
• vector: arrow to represent a force * length: magnitude (size of the force)
• Arrow head: indicates direction
• Shaft: line of application