# Motion and Kinematics

TIP:  The displacement of an object is NOT the same as the distance the object travels!

TIP:  The average speed of an object is NOT the average velocity.  Since velocity (and displacement) are vector quantities, they can equal zero while there is still an average speed for the entire trip.

TIP:  The average speed of an object is NOT the average velocity.  Since velocity (and displacement) are vector quantities, they can equal zero while there is still an average speed for the entire trip.

TIP:  The slope of the line tangent (ratio of vertical to horizontal quantities) to the distance-time curve of a graph is defined to be the instantaneous velocity at that time.

TIP:   Negative acceleration does not necessarily mean an object is slowing down.   If the acceleration and the velocity are both negative, the object is speeding up.

TIP:   Always go back and check your answers for reasonableness.   Does your number make sense?   Should it be larger or smaller?

## SUMMARY

1. Displacement – change of position in certain direction from starting point; vector quantity
2. Vector quantities – have magnitude and direction
3. Average velocity – displacement/time; equal to the slope of the straight line joining the initial and final points on a graph of distance/displacement vs time
4. Instantaneous velocity – slope of the line tangent to the displacement-time curve at any point
5. Instantaneous speed – the magnitude of the instantaneous velocity
6. Instantaneous acceleration – slope of a velocity-time graph at any instant
7. Average acceleration – change in velocity divide by the time interval during which the change occurs
8. As objects fall to Earth, they experience a freefall acceleration directed toward Earth’s center (because of the pull of gravity)
9. For all practical purposes, the acceleration due to gravity is constant (neglecting air resistance) and is equal to g = 9.80 m/s2

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