Velocity time graphs

• can be used to show uniform and non uniform acceleration of a car traveling along a straight line in one direction

Velocity time graphs: gradient gives acceleration of object

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Describing velocity time graphs

1. Direction. + or -, left or right, up or down
2. Acceleration - constant / uniform / increasing / decreasing  When describing, do your best to squeeze in some actual numbers from the graph

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When is displacement negative for velocity time graph?

• When the negative region of the graph is greater than the positive region. 
• Negative displacement is greater than the positive displacement.

Meaning of negative velocity:

• Object moves in the other direction from which it started.

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- Velocity of car remains at 0, car has 0 acceleration as gradient = 0.  - Area under graph is 0, displacement is constantly 0, stationary	- Velocity remains at 10m/s - uniform velocity.  - Car has 0 acceleration as gradient equal to 0.  - Positive direction from starting point [check]
- Velocity of car increases by 10 m/s every second - Graph has positive and constant gradient, acceleration is uniform/constant - Moves in a positive direction from the starting point.	- Velocity of car decreases by 10 m/s every second - Graph has negative and constant gradient, and there is acceleration in the negative direction (deceleration) - Object is still moving in the positive direction away from the starting point, but the object has acceleration in the negative direction. (slowing down)
- Increase in velocity of car is increasing with time - Graph has positive and increasing gradient, acceleration increases - Moves in a positive direction from the starting point.	- Increase in velocity of car is decreasing with time - Graph has a positive and decreasing gradient, and acceleration decreases. - Moves in a positive direction from the starting point.

Unaccepted phrasing

• constantly accelerating
• Rate of acceleration is constant

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Area under Velocity Time Graph

⇒ returns displacement

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Speed time against graph against velocity time graph

assign upward direction from ground as positive

Speed/time graph	Velocity/time graph
$A_1$ → distance traveled h during its upward journey to the highest point.  $A_2$→ distance traveled h during its downward journey from the highest point.  For speed-time graph: Total distance traveled by volleyball = total area under the speed time graph $A_1+A_2=h+h=2hm$	$A_1$ → displacement is positive during its upward journey to the highest point $A_2$ → displacement is negative during its downward journey from the highest point. For velocity time graph: Total displacement of volleyball = total area under velocity time graph  $A_{}1+A_{}2=h+(-h)=0m$
Acceleration of free fall
Galileo’s finding - all objects, regardless of mass or size, fell at the same acceleration due to earth’s gravity

Acceleration due to gravity / gravitational field strength g is a constant.  Value of g is taken to be $10m/s^2$

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