# Evan's Space

## Wonders of Physics # Velocity-time and Displacement-time graph for Ball thrown up and comes down

A ball is thrown vertically upwards from the hand and lands back onto the hand. It is important to note that once the ball leaves the hand, the  resultant force acting on the ball is only its weight! And it is acting downwards throughout the motion.

Velocity-Time Graph

Displacement-Time Graph

Key points to note when sketching the v-t graph:
1) Fixing the direction up to be positive (can be down as positive if you want)
2) At t = 0s, the initial velocity of the ball is maximum.
3) As it goes up vertically, due to the weight acting downwards, the ball decreases in speed (decelerates)
4) At the highest point, the ball is momentarily at rest (v =0m/s)
5) On the way down, due to the weight of the ball acting downward, the ball accelerates downwards.

### 13 thoughts on “Velocity-time and Displacement-time graph for Ball thrown up and comes down”

1. Why the velocity of the ball is negative when it accelerates downwards ?

• Velocity is a vector quantity. So direction is important. As up is set as positive, when the ball is thrown up the velocity decreases. It is positive velocity as it is moving upwards. When it is falling downwards, the velocity increases but it’s negative, indicating that the speed is going faster but in the opposite direction. Negative velocity just means direction is opposite. Hope this helps

• How comes that the acceleration in upward and downward movement is negative

• Because we fixed up as positive. As velocity decreases as it goes up so it is deceleration (negative acceleration). But as it is coming down, the direction is opposite to just now. Thought it’s speed increases as it comes down, due to moving in opposite direction, the acceration is negative

2. is acceleration negative throughout the motion?

3. Yes. If you set upwards direction as positive

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