Lesson 4: Test your Knowledge on Laws of Motion – Part 5

Scene 4: Twilight Car Block 

Watch a scene from the movie “Twilight” in which one of the characters saved another by putting his hand out and stopping a vehicle out of control. Answer the following questions:

What Laws of Motion are broken?

What should have happened?

Give a breakdown of the circumstances in the scene in relation to the equation Force equals mass times acceleration (F = ma). For example, is the mass of the person small compared to the car?

 Based on this breakdown, what would the character that stopped the car need to actually stop the car in real life? 

https://www.youtube.com/watch?v=KrBQNiN8ifY 

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

This scene illustrates the Second and Third Newton’s Laws of motion. In this scene Edward saves Bella from an out of control car. Consider the Second law, which states F = ma. The mass of Edward is smaller than the cars, and his acceleration is also negligible when compared to the car; therefore the force from the car should by all means be higher than the force from Edward. Instead the scene shows that the car’s surface bends around the area where he placed his hand, suggesting his force was much larger than the car’s. Edward should have been sent backwards due to the impact. The fact that this did not happen mean that, since his mass is smaller than a car’s, his acceleration must have been high enough to overcome the difference in mass. If you look at the scene though, he stops in front of Bella and just puts his hand in the direction of the car; this means a lack of acceleration in the direction of the car (note that he was running perpendicular to the direction the car was coming, so he could not have any acceleration in that direction regardless of running). If he had been running (and accelerating) in the direction of the car’s axis and then pushed the car like that, it would be possible assuming he was going really fast.