EXAM Flashcards
what does coefficient of friction represent ?
A measure of the amount of friction existing between two surfaces.
Instantaneous Velocity
-a continuous function of time and gives the velocity at any point in time during a particles motion.
-Velocity of an object under the motion in a point of time
Acceleration
is the rate the change of the velocity of an object with respect to time
-allows you to measure how fast velocity changes in meters per second squared
Tangent Line of a Curve
-a straight line that “just touches” the curve at that point
-the slope of the tangent line is then a distance travelled divided by an elapsed time and can thus be interpreted as a velocity.
displacement
the shift in location when a object in motion changes from one position to another
Visual estimation of velocity
Forward direction is Positive
Backward direction is negative
visual estimation of acceleration
Acceleration is independent of the direction of motion. Both positive and Negative accelerations can result without the object changing direction.
Shuttle Run Position-Velocity-Acceleration
SAME SIGN:
-acceleration is positive when accelerating (increasing speed)
-acceleration is negative when decelerating (decreasing speed)
-Velocity is positive when going in one direction
-Velocity is negative when going in opposite direction.
Shuttle Run Position-Velocity-Acceleration
VELOCITY IS ZERO
-velocity is zero because the runner is switching direction
Shuttle Run Position-Velocity-Acceleration
ACCELERATION IS ZERO
-is zero when speed is constant
-when runner/person is neither decelerating or accelerating.
Relative Joint Angle
-is the angle between two longitudal axes of two segments
-this will not describe the position of the segment in space
-three points of interest needed; proximal, vertex, and distal points
Absolute Angles
-the angles of inclination of a body segment relative to some fixed reference in the environment
-Two points of interest: proximal and distal
Segment Angle
The angles calculated relative to right horizontal is called segment angle
Angular Motion
measured relative angle is compared to angle of joint in the anatomical position
Hip Angular motion: 180-relative angle of hip
Knee Angular motion: 180-relative angle of knee
Ankle Angular motion: 90-relative angle of ankle
Gait
Purpose: to get from one point to the next major motor functions
- Maintenance support of the upper body
- Maintenance of an upright posture and balance of the HAT head, arm, trunk
- Control of foot trajectory for ground clearance and gentle heel/toe landing
- Generation of mechanical energy to maintain velocity
- Absorption of mechanical energy for shock absorption and stability or to decrease velocity
Single Support Phase
is also known as the swing phase where only one limb is in contact with the ground
-occurs between the heel strike of one foot and the toe off of the opposite foot.
Double Support Phase
Portion of walking cycle when both feet are in contact with the ground simultaneously
-occurs twice during each gait cycle, once when the first foot makes contact with the ground (heel strike) and the second foot begins to make contact, AND again when first foot Is lifting off the ground (toe off) and the second foot remains in contact.
Gait Parameters - Stride Length
distance between successive points of initial contact of the same foot
Gait Parameters - Step Length
distance between point of initial contact of one foot and the point of initial contact of the opposite foot
Gait Parameters - Step Width
lateral distance between successive points of opposite feet
Gait Parameters - Foot angle
describes an angle between the line of progression and a line drawn between the midpoints of the calcaneous and the second metatarsal head
Centre of Mass
is considered the point about which the body is evenly ditributed
Free Body Diagrams
A free body diagrams is the link between the complexity of the human situation and the application of the limited, although powerful, techniques of mechanics
FBD trying to figure out
1) The joint reaction force
2) The muscle force needed to hold the position
FBD Assumptions
1) Static
2) All forces are acting in the same 2D plane
3) Joints are considered hinge joints
4) Muscles under consideration are represented as single muscle equivalent
5) Unknown forces are acting in positive direction
