Multi-Ball Collision
Demonstrate the theory of momentum conservation and the concept of coordinates system.
What?
Demonstrate the theory of conservation of momentum and the concept of coordinate systems.
How?
Let two balls of different masses make one dimensional impact in the vertical direction.
- Drop two balls, one larger and heavier the other smaller and lighter, from the same level and let them free fall to the ground.
- Observe the heights they bouncing to.
- Put the smaller ball on top of the larger ball and keep the centers of these balls in a vertical line, as close as possible. Release these balls and let them free fall to the ground.
- Observe the heights they bouncing to.
×Experiments demonstration
Why?
Why is the small ball bouncing to a height so different from before?
×Think...
When these two overlapped balls impact the ground, the large ball has velocity V relative to the ground, the relative velocity from the large ball to the small ball is 2V (see figure 2 and 3). So, when the small ball is bouncing back, its velocity is 3V relative to the ground (see figure 4). Hence the height is proportion to the square of velocity (
Figure 1. Before first Impact (use the ground as reference coordinates)
Figure 2. Before second Impact (use the ground as reference coordinates)
Figure 3. Before Second Impact (use the larger ball as reference coordinates)
Figure 4. After Second Impact (use the ground as reference coordinates)
Questions
- Put the large ball on top of the small ball and set free to fall. How high will these two balls bounce up?
- Try to examine the relative motions of this system with the reference coordinates fixed on the large ball. If the mass difference of these two balls is very large (says 10 times), to an observer on the ground, the bouncing velocity of the smaller ball will be how many times of the impact velocity? The bouncing height will be how many times of the original height?
Reference
- Jay S. Huebner and Tarry L. Multi-ball collision, Phys. Teach. 30, 46 (1992)
Producer
v.1 Jhih-Hua He（何治樺）
v.2 Tsung-Cean Tu （杜宗勳）, Ching-Chi Chu （朱慶琪）
Experiment Materials
Basketball and tennis using in experiment can buy it from sports stores and stationers.
Advisor
Ching-Chi Chu （朱慶琪）
Written by
v.1 Jhih-Hua He（何治樺）
v.2 Tsung-Cean Tu （杜宗勳）, Ya-Chen Li （李亞宸）, Ching-Chi Chu （朱慶琪）
