Ball 1 was released and traveled down the ramp to hit the stationary ball (Ball 2) placed in the middle of the ramp. After the collision: Ball 1 ceased moving forward briefly but continued to spin, then continued up the ramp following the path of the second ball; Ball 2, once hit, moved up the ramp. Both balls collided again on their way back down the ramp before finally coming to a stop in the middle.
The two balls represent the different type of kinetic energy. Ball 1 represents both rotational and translational energy as it is coming down the ramp. Once it hits Ball 2, the energy splits, Ball 1 retains the rotational energy causing it to stop, spin and later travel up the ramp. Ball 2 exhibits translational energy, gaining the momentum to travel up the ramp from it’s stationary position.
The challenge!
-
Can you determine the ratio of energy that the 1st ball (Ball 1) had in terms of Rotational Kinetic Energy (Energy of Spinning) and how much the 1st ball had in terms of linear Kinetic Energy? Describe how you could figure it out.
In order to figure out the ratio of energy, it is important to first know the height that each ball reaches when exhibiting the appropriate type of kinetic energy. Rotational energy lasted a distance of 4.5 cm. Translational energy traveled 42 cm. Together, this results in a total of 46.5cm. The ratios used to figure out the percentage of energy that each type exhibits is as follows:
Rotational Translational
4.5cm _ = .0967 * 100% = 9.7% 42cm _ = .9032 * 100% = 90.3%
46.5cm 46.5cm
Reflection Questions:
- How does this experiment relate to the energy that the Earth has as it orbits around the Sun?
This experiment shows a relationship to the energy of the Earth in the form of momentum and gravitational pull as it orbits around the Sun. The momentum of the Earth was established when the Earth was formed and the Sun exerts gravitational pull on the Earth. Therefore, the Earth doesn’t travel in a straight line, but it spins around the Sun. This relates to the experiment we did because the balls have momentum, just like the Earth.
-
As you probably noticed during this experiment the ball does not reach the same height from which it was dropped. This is due to non-conservative forces like friction. We also know that the Earth rotation is slowing down. For example, the Earth’s day was once about 20 hours rather than today’s 24 hours. What (or where) do you think is the force that is removing energy from the Earth’s rotation? Describe why you think “your answer here” force?
The Earth’s rotation has been consistent due to momentum. However, in order to impact and influence that force, another force would have to have acted upon the Earth at some point in its history. One possibility of an outside force is the hypothesized meteor that hit the Earth millions of years ago and caused the extinction of the dinosaurs. If it entered Earth’s atmosphere and crashed into the planet at a particular angel in relation to the spinning Earth, then it could very well have transferred energy in the opposite direction of the rotation of the Earth. The meteor was smaller than the Earth, so it’s energy was not enough to completely stop the Earth from spinning or cause it to change direction, however it might have removed enough energy from the Earth’s rotation to cause it to spin more slowly.
-
What do you think would happen if the first ball (Ball 1) was much heavier than the 2nd (stationary ball 2?). Feel free to do an experiment to find out!
Upon impact, both balls travel up the ramp with the smaller ball going just a little farther than the heavier ball. The balls travel back down together, settling at the middle of the ramp.
- What did you learn from this investigation?
When Ball 1 is heavier than Ball 2, the heavier ball transfers only so much energy as the lighter ball can absorb; the smaller ball can only absorb so much energy. The larger ball is retains the energy that does not transfer (since total energy is always the same in the system), so Ball 1 keeps the translational and rotational energy that does not get absorbed by Ball 2. This allows Ball 1 to continue up the ramp while spinning. Energy takes into account the weight of an object, and as a result, the larger and heavier ball holds more energy.
