# Question on Laws of Motion observed in Real Life

1. Jan 18, 2014

### rajumahtora

When I had a school tour to A water park, there I observed that when a heavy boy used to slide down a water slide(and stop at β), he used to go further than where the ligher boy used to stop after sliding(α).
But the friction will act more on Heavier then why is he going further?

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2. Jan 18, 2014

Assuming both the heavy boy and lighter boy are moving with the same velocity, I think its probably because the heavy boy will have more momentum than the lighter boy, p=mv, thus as compared to the lighter boy more friction will be required to stop the heavy boy.Therefore he travels farther.

3. Jan 18, 2014

### Staff: Mentor

You're right about the frictional force: It's proportional to the normal force between boy and slide, and that's proportional to the weight so should stop them both at the same point.

That's not what you've observed, so you have to conclude that there is some other force at work as well, one that is not proportional to the weight so Heavy's momentum will carry him farther against that force. Air resistance is a good candidate, and on a water slide fluid resistance from the water is also possible.

Last edited: Jan 18, 2014
4. Jan 18, 2014

### Staff: Mentor

Was the light boy wearing a pool shirt and the heavy boy not wearing a pool shirt? This has a big frictional effect on water slides if the people are lying down.

5. Jan 18, 2014

### sophiecentaur

Your terminal speed will depend upon the resultant of your weight force and the resistance forces. The larger boy will have much greater weight force but very similar resistance forces. There are other factors at work when they use different mats or clothing or learn the speed technique of holding their body in the optimum shape.

The simple laws of motion assume no friction so they predict the same acceleration and final speed for both boys. Taken to extremes, in a practical situation, the terminal velocity of a mouse, falling through air, is low enough for it to be thrown off the Empire State Building and for it to walk away from the experience. Unlike the situation for an elephant. (Not Dumbo, of course)