Energy and Cannons

I'm back for yet another awesome post! My class decided to write a post about Energy and Conservation of Energy in real world example. We also decided that we should use online tools, such a Glogster here, to create a story around the example. So, let me tell you a story about a freshman physics student who used his knowledge for a good cause...

Tools used (also stated in the Glogster):

Glogster

Equation Editor

Cosketch

Physics Mythbusters

This new lab was quite possibly the best lab yet. As you can see from the title, we attempted to "bust" two different myths about the general facts of physics, using tools such as video and online drawing tools. I will explain what the myths are in each myth's section. So, are they true? Let's find out

Myth 1:

An object always moves in the direction of the net force exerted on it.

Materials: tennis ball, baseball bat, and Flip Video camera

Procedure:

1. Set up the video in an open area, power on the Flip Video camera and begin recording.

2. Throw the tennis straight up, let it bounce off the ground and begin to fall again.

3. Hit the tennis ball with the baseball bat in the way a batter would hit a baseball.

4. Upload the video to a computer.

5. Analyze the video and draw FBD's.

6. Using the video and the FBD's, decide whether the myth is busted or confirmed.

Prediction:

If an object always moves in the direction of the net force and we are hitting a tennis ball with a baseball bat, then immediately after the tennis ball leaves the bat, it show move towards the area between the bat and the ground, due to the net force of air resistance and free-fall pointing in that direction.

FBD:

Sum of the Forces:

Confirmed or Busted?

After the ball leaves the bat, it is moving in the opposite direction of the net force. Therefore, the myth is busted.

Myth 2:

An object always changes its motion if there s a force exerted on it by other objects.

Materials: 2 people, and a Flip Video camera

Procedure:

1. Set up in a fairly large area clear of obstacles, power on the Flip Video camera, and begin recording.

2. Set the two people around 15 ft apart facing each other.

3. Have one begin to sprint towards the other, trying to accelerate throughout the entire experiment.

4. The sprinting person will then sprint straight into the standing person, knocking him or her over.

5. The sprinting person will keep on trying to accelerate after they knock the standing person over.

6. Upload the video to a computer.

7. Analyze the video and draw a FBD of the sprinting person te momentwhen they hit the standing person.

8. Using the video and the FBD, determine whether the myth is busted or confirmed.

Prediction:

If an object always changes its motion when there is a force exerted on it by other objects and one person runs into another person, then the running person will change his or her motion, and change direction.

FBD:

Sum of the Forces:

Confirmed or Busted?

The sprinting person never changed direction. Therefore, the myth is busted.

Conclusion:

So obviously, these two myths are, in-fact, misconceptions. To someone not in the know about physics, they do seem true however. It is quite clear how these people may think so. They may think that forces instantly affect the direction of something and immediately reverse or alter its course. What force affect, however, is acceleration. An object will ACCELERATE in the direction of the net force. It is only when the acceleration brings the objects velocity to zero then will the object begin to move in the direction of the net force. Also, if an object maintains an acceleration throughout another force being exerted on it, it will not change its motion or direction. These myths are quite confusing. It is really easy to think them as true.