Lecture 3 - Kinetic Framework

Question 1

Scalars

Answer 1

Measures that just have a value, size, etc.

Only magnitude, no direction

These can be added by just summing the numbers (10kgs + 10kgs = 20kgs)

Question 2

example of Scalars

Answer 2

Examples: mass, volume, length, and speed

Question 3

Vectors

Answer 3

Measures that involve both magnitude and direction

Note: Typically illustrated by an arrow

Question 4

Kinetic vector quantities:

Answer 4

force, weight, pressure, and torque

Question 5

Kinematic vector quantities:

Answer 5

displacement, velocity, and acceleration

Question 6

Can you add Vectors like Scalars?

Answer 6

You cannot simply add vectors together like scalars, you have to take into account the direction

Question 7

Resultant vector:

pg. 6

Answer 7

when you add two vectors together

The resultant vector goes from the tip of one vector to the tail of the other

Question 8

How do you figure out the resultant vector

Answer 8

1. Use the pythagorean theorem to get the length of the resultant (or hypotenuse); a^2 + b^2 = c^2
2. Magnitude would be equal to the side length
3. To get a direction of the vector, we need to figure out the angle
4. To find the angle, use inverse cos/tan/sin

Question 9

Resolving (Splitting) Vectors

Answer 9

1. You can split the resultant into two vectors typically 90 degrees from each other (a horizontal and vertical component)
2. You need to know the angle to split the resultant
3. To find this, use the sin/tan/cos functions

Question 10

Inertia

Answer 10

The tendency for a body to resist a change in its state of motion

Resisting the acceleration, or motion

Question 11

True or False: It is harder to accelerate something with a larger mass as opposed to a smaller mass

Answer 11

true

Question 12

Inertia Has no unit of measurement

Question 13

The amount of inertia an object has is directly proportional to its mass

Question 14

Mass definition:

Scalar or Vector:

Symbol:

Units

Answer 14

A quantity of matter contained in an object

Scalar

m

kilograms(kg)

Question 15

Force definition:

Scalar or Vector:

Symbol:

Units:

Answer 15

A push or pull acting on an object that causes or attempts to cause a change in the motion of a body

Vector

F

newtons (N)

Question 16

Common Forces in Human Movement

Answer 16

Internal forces
External forces

Question 17

Internal forces

Answer 17

Muscle force

Joint force (Ligament forces; bone on bone)

Question 18

External forces

Answer 18

Gravity (weight) (lack of gravity changes how people move)

Ground reaction force (reaction between foot and ground)

Friction

Question 19

Net Force Definition:

Units:

Symbol:

Answer 19

Force resulting from the vector addition of two or more forces

newtons (N)

∑F (sum of forces)

Question 20

Weight Definition:

Magnitude formula:

Direction of Weight:

Point of application:

Units:

Symbol:

Answer 20

Force due to gravity (the amount of gravitational attraction between object and earth)

Fg = m x ag
, where ag = acceleration due to gravity (9.81 m/s^2 on earth)

downwards

centre of gravity

Newtons (N)

Fg (force of gravity); textbook uses ‘wt’

Question 21

Centre of Gravity Definition:

Centre of Gravity Concept:

Answer 21

The point about which a body’s weight is equally balanced, no matter how the body is positioned

where all the weight of a body is considered to be concentrated at a single point and acts downward from that point

Question 22

“If a scale shows that an individual has a mass of 68kg, what is their weight?”

Answer 22

Known: m = 68kg
Wanted: weight (Fg)
Formulas: Fg = m x ag
Answer: Fg = 68kg x 9.81 m/s^2 (= 667 N)

Question 23

Torque Definition:

Answer 23

A rotary effect of a force (also called moment of force)

Causes or attempts to causes a change in the rotational motion of a body

It is the torque of muscles that cause us to be able to move

Question 24

Magnitude of torque formula:

Direction:

Symbol:

Units:

Answer 24

T = F x d (force x moment arm)

clockwise or counterclockwise around the axis of interest (at joint use joint movement terms such as flexion or extension)

T (will sometimes see M for Moment)

newtons meters (N.m)

Question 25

Moment Arm Definition:

Symbol:

Units:

Answer 25

The perpendicular distance from the line of action of the force to the location of the axis of interest (typically at centre of gravity of a system or at a joint)

d (often just showed as “d”)

metres (m)

Question 26

Free Body Diagram

Answer 26

A sketch that shows a defined system in isolation with all of the force vectors acting on the system

Question 27

Impulse Definition:

Magnitude:

Units:

Answer 27

The integration of force over time

the area under a force vs. time curve (if force is constant, impulse = F x t)

newton seconds (N.s)

Question 28

Tools for Measuring Kinetic Quantities

Answer 28

Electromyography (EMG)
Force Plates
Other force gauge examples

Question 29

Electromyography (EMG):

Answer 29

➢ To study neuromuscular function
➢ Estimate of muscle activation
➢ Not a direct measure of force

Question 30

Force Plates:

Answer 30

➢ To measure ground reaction force
➢ Primarily employed in gait research
➢ A scale

Question 31

Other force gauge examples:

Answer 31

Handgrip dynamometer
Fish scale