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Mechanics
Motion
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Quantity |
Definition |
Vector/
Scalar
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S.I. Unit |
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Displacement |
distance moved in a specified direction |
v |
m |
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Speed |
distance moved per unit time |
s |
ms-1 |
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Velocity |
distance moved per unit time in a specified direction |
v |
ms-1 |
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Acceleration |
change in velocity per unit time |
v |
ms-2 |
The Equations of Motion
These equations are useful for solving problems in which objects are moving
with uniform acceleration.
If the sense of the motion changes, decide which sense is
positive before starting the calculations.
| t |
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represents time |
| a |
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represents acceleration |
| u |
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represents "initial" speed (or velocity) |
| v |
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represents "final" speed (or velocity) |
| s |
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represents
the displacement from some
reference point (usually the starting
point) at time t.
If the reference point is not the starting
point, we might also see so in the
equations (where so means the displacement
at time t = 0). |
The equations will give us the magnitude and sense
of the velocities, accelerations and displacements.
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1. Average velocity, |
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so |
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2. Acceleration, |
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3. Equation 2 is often rearranged to give: |
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4. Combining equations 1 and 3 in order to eliminate v gives: |
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5. Combining equations 2 and 4 in order to eliminate t gives: |
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Displacement against Time Graphs
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a) stationary
b) uniform velocity |
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uniform acceleration |
The slope of a s/t graph represents velocity.
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