# Average force of friction

1. Jun 7, 2005

### Frank_Horrigan

Question: Determine the average force of friction over the first drop and over the entire trip from top to bottom.

This is a question of have from a lab experment which was when we designed a "roller coaster" for a ball (it was a downwards ramps with 2 humps on it). I have the actual velocitys at all points in time that I recorded, and I calculated the theoretical speed of the ball at these 2 points by using the law of conservation of energy and calculating Ek. My question is what is this question asking? What does the "average force of friction" mean?

2. Jun 7, 2005

### brewnog

Well I think it's a bit vague, because your ball was rolling and not sliding.

However, you should be able to calculate the overall force acting in the direction opposite to motion, which will be a combination of friction and air resistance.

I suggest you use your knowledge of the principle of conservation of energy in order to work out what amount of energy was lost over the course of the roller coaster.

3. Jun 7, 2005

### Frank_Horrigan

brewnog thanks for that, I had already found out the amount of energy lost to friction for the two point. To do that i subtracted the actual kinetic energy and the gravitational energy from the initial gravitational energy, which will give me the amount of energy lost to friction. However this question asks for the average force of friction, which I think has to be in newtons but I dont know what it means or how to calculate it.

I've calculated I lost 0.071J to friction after first drop, what do i do with this to get average force of friction?

Last edited: Jun 7, 2005
4. Jun 7, 2005

### brewnog

Do you know any relationships between work done, forces and distances?

5. Jun 7, 2005

### Frank_Horrigan

Do you mean W=Fxd ? If I used that i would already have W and I would be solving for F right, ok sweet I think I'm almost there now but I cant think of a way to calculate d, because it is a rollercoaster path, so its all curved and such. Maybe if i averaged the velocitys over that time and multiplied it by the time?

Or does that way of gettint the veocity not work since acceleration is not a constant? An example of what i mean is that the initial velocity could be 0, it could then travel down the ramp and then up a hump and then again get a velocity of 0, but its average velocity during that time was not 0 even tho 0+0/2=0

Scratch that I thought about it and it wouldn't work just like I thought before, now I'm trying to think of another way to calculate the distance.

After thinking about it I think it is impossible to calculate the distance isnt it? This project isnt due until friday so I guess I'll have to go in and manually measure the roller coaster.

Last edited: Jun 7, 2005