Lecture 3 - Kinetic Framework Flashcards
Scalars
Measures that just have a value, size, etc.
Only magnitude, no direction
These can be added by just summing the numbers (10kgs + 10kgs = 20kgs)
example of Scalars
Examples: mass, volume, length, and speed
Vectors
Measures that involve both magnitude and direction
Note: Typically illustrated by an arrow
Kinetic vector quantities:
force, weight, pressure, and torque
Kinematic vector quantities:
displacement, velocity, and acceleration
Can you add Vectors like Scalars?
You cannot simply add vectors together like scalars, you have to take into account the direction
Resultant vector:
pg. 6
when you add two vectors together
The resultant vector goes from the tip of one vector to the tail of the other
How do you figure out the resultant vector
- Use the pythagorean theorem to get the length of the resultant (or hypotenuse); a^2 + b^2 = c^2
- Magnitude would be equal to the side length
- To get a direction of the vector, we need to figure out the angle
- To find the angle, use inverse cos/tan/sin
Resolving (Splitting) Vectors
- You can split the resultant into two vectors typically 90 degrees from each other (a horizontal and vertical component)
- You need to know the angle to split the resultant
- To find this, use the sin/tan/cos functions
Inertia
The tendency for a body to resist a change in its state of motion
Resisting the acceleration, or motion
True or False: It is harder to accelerate something with a larger mass as opposed to a smaller mass
true
Inertia Has no unit of measurement
The amount of inertia an object has is directly proportional to its mass
Mass definition:
Scalar or Vector:
Symbol:
Units
A quantity of matter contained in an object
Scalar
m
kilograms(kg)
Force definition:
Scalar or Vector:
Symbol:
Units:
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)
Common Forces in Human Movement
Internal forces
External forces
Internal forces
Muscle force
Joint force (Ligament forces; bone on bone)
External forces
Gravity (weight) (lack of gravity changes how people move)
Ground reaction force (reaction between foot and ground)
Friction
Net Force Definition:
Units:
Symbol:
Force resulting from the vector addition of two or more forces
newtons (N)
∑F (sum of forces)
Weight Definition:
Magnitude formula:
Direction of Weight:
Point of application:
Units:
Symbol:
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’
Centre of Gravity Definition:
Centre of Gravity Concept:
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
“If a scale shows that an individual has a mass of 68kg, what is their weight?”
Known: m = 68kg
Wanted: weight (Fg)
Formulas: Fg = m x ag
Answer: Fg = 68kg x 9.81 m/s^2 (= 667 N)
Torque Definition:
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
Magnitude of torque formula:
Direction:
Symbol:
Units:
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)
Moment Arm Definition:
Symbol:
Units:
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)
Free Body Diagram
A sketch that shows a defined system in isolation with all of the force vectors acting on the system
Impulse Definition:
Magnitude:
Units:
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)
Tools for Measuring Kinetic Quantities
Electromyography (EMG)
Force Plates
Other force gauge examples
Electromyography (EMG):
➢ To study neuromuscular function
➢ Estimate of muscle activation
➢ Not a direct measure of force
Force Plates:
➢ To measure ground reaction force
➢ Primarily employed in gait research
➢ A scale
Other force gauge examples:
Handgrip dynamometer
Fish scale
