MEDI 11002 Lecture Notes - Lecture 1: Net Force, Potential Energy, Clothes Dryer
ANALYSING MOTION
Vectors and scalars
- A scalar quantity is fully described by magnitude only
- A vector quantity can only be fully described by giving both magnitude and
direction
o Vector addition is represented by arrows whose lengths represent the
magnitude and arrowheads represent direction
o Vectors are added geometrically. The resultant is the vector which begins at
the tail of the first vector and ends at the arrowhead of the second.
o They have a horizontal and vertical component
Describing motion
- Displacement – distance moved in a particular direction (as measured in a
direct line from the origin)
- Distance – how far a body has travelled, irrespective of direction (displacement
in these cases could be zero)
- Speed – the rate of change of position
- Velocity – the rate of change of the position in a particular direction
- Acceleration – the rate of change of velocity in a particular direction
Calculating speed, velocity and acceleration
- The average speed provides and overall description of the motion and does not
indicated variations of speed that may have occurred during time under
consideration
- Instantaneous speed is the actual speed at a particular moment.
o *When the time interval tends to zero
- Average speed compared to average velocity:
- Acceleration – change in the velocity; is given by:
Measured in ms-2
o Instantaneous acceleration:
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Equations of motion:
Graphical analysis of motion
1. Displacement-time graph – slope of the graph indicates velocity
2. Velocity-time graph – slope of the graph indicates acceleration; area under the
graph indicates displacement
Newton’s laws of motion and momentum
- Law 1 – a body continues in its state of rest, or of uniform motion in a straight
line, unless acted upon by an external unbalanced force
- Law 2 – the rate of change of the momentum of a body is proportional to the
applied force and occurs in the direction of that force
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Document Summary
A scalar quantity is fully described by magnitude only. A vector quantity can only be fully described by giving both magnitude and direction: vector addition is represented by arrows whose lengths represent the magnitude and arrowheads represent direction, vectors are added geometrically. The resultant is the vector which begins at the tail of the first vector and ends at the arrowhead of the second: they have a horizontal and vertical component. Displacement distance moved in a particular direction (as measured in a direct line from the origin) Distance how far a body has travelled, irrespective of direction (displacement in these cases could be zero) Speed the rate of change of position. Velocity the rate of change of the position in a particular direction. Acceleration the rate of change of velocity in a particular direction. The average speed provides and overall description of the motion and does not indicated variations of speed that may have occurred during time under consideration.