# Convert velocity to newtons?

1. Oct 9, 2005

### NutriGrainKiller

Working out some simple physics and I can't figure out how to convert velocity to newtons for force..

A six pound (2.72kg) tonka truck is moving across a cardboard bridge at a constant velocity of .067m/s (estimated). I tried looking for a while but was unable to find the kinetic friction of plastic wheels on cardboard.

Using newton's second law, I was able to make this equation: F-Fk=ma, so F = ma+Fk. Fk is muK*Fn, so the final equation is: F=ma+muK*fn. Because there is no movement in the Y direction, fn would be the weight, and in this case 26.7n. there is no acceleration, so would ma equal zero?

Is there any way to find the kinetic friction between plastic and cardboard?

Thanks guys!

2. Oct 9, 2005

### arildno

Not surprising, since you can't "convert" velocities into forces in the first place.
What do you mean by this?

3. Oct 9, 2005

### NutriGrainKiller

Well I think I answered that in my initial post, however there are more questions further down

4. Oct 9, 2005

### Staff: Mentor

What exactly are you trying to figure out? Is the truck moving at constant velocity? Are the wheels rolling?

5. Oct 9, 2005

### Pengwuino

It is really something you'd have to look up and you'd have to know the exact dimensions of what the tire is that is actually touching the ground.

Also, as arildno pointed out, velocity and force are two different things. It is like comparing temperature to density.

6. Oct 9, 2005

### arildno

You can't convert a velocity into a force! Period.

7. Oct 9, 2005

### NutriGrainKiller

i figure i can find out the force with the coeffecient of kinetic friction between cardboard and plastic wheels, any way i can do this?

8. Oct 9, 2005

### Staff: Mentor

Realize that if the car is moving at constant velocity, the net force is zero. Also, if the wheels are rolling (not slipping) then kinetic friction will not apply. And the static friction will be zero as well.

9. Oct 9, 2005

### Gokul43201

Staff Emeritus
From the power output of the motor that's driving the truck (and the velocity) you can find the driving force, using P = Fv