Lesson 4: Test your Knowledge on Laws of Motion – Part 2

Scene 1: Speed Bus Jump 

Watch the famous scene from the movie “Speed” in which the bus jumps over a large gap on an incomplete bridge and somehow manages to make the jump. Click on the link below to start watching. Try to answer the following questions:

What Laws of Motion are broken?

Can such a jump be made in reality?

What would actually happen to the bus? What is the cause for the real case scenario?

Assume that there was a ramp at x angle at the end of one side of the bridge; would the bus then be able to make the jump? In that situation, would the speed of the bus increase or decrease as it jumps from one side? Would it remain constant?

Click here to read a discussion on the scene and compare your thoughts.

This scene illustrates the First and Second Newton’s Laws of motion. In this scene, we have a bus jumping over a large gap, which is stated to be 50 ft. in length. If you look at the video, the bus appears to jump off the bridge at an incline, which suggests that there is a ramp at the end of their side just as they make the jump. Of course, that does not make sense since roads would not contain such ramps, so this is the first inconsistency in this scene. 

In terms of laws of motion, the first law indicates that an object will continue in a straight line at constant velocity with no external forces acting on it. Assume for a moment that there are no external forces on the bus and so it moves straight into the ledge; once the front wheels go over the ledge, what should happen? The bus will begin inclining downward due to gravity; this can be seen in the free body diagram. 

For the second law, consider that while on the road, the force of gravity is cancelled by the upward normal force of the road on the bus, however once part of the bus goes over the gap, gravity starts taking effect since there is no longer any normal force being applied upward. Due to this behavior, the only way for the bus to make the jump is if the other end of the road is at a lower height than the end they are jumping off. 

So what would it take for the bus to make the jump? Look at this video to find out. 

(http://www.escapistmagazine.com/videos/view/reel-physics/7126-Speed-CalTrans-is-Bus-Ted