# Force of a car

1. Nov 5, 2007

### redsox5

If I have a small model car and use a spring scale to measure the force, my reading is .130 kg. How do convert that to Newtons? Is gravity relevant to this equation?

I know that F = m x a

the mass of the car is .387 kg
is the accerleration the acceleration of the car or gravity?

2. Nov 5, 2007

### Integral

Staff Emeritus
To get Newtons multiply the mass in Kg by g, the acceleration due to gravity, 9.81 $\frac m {s^2}$

3. Nov 6, 2007

### noagname

now how do you calculate the amount of force it would take to push that car

4. Nov 8, 2007

### summerzhuling

Is that a test?

5. Nov 8, 2007

### noagname

6. Nov 10, 2007

### jdogg0075

I don't know if this is a question of your own or what. But any case:
On a frictionless surface any amount of force would move the car. Now when you introduce friction You would have to take into account the coeff. of static friction and normal force (weight of car in newtons).

7. Nov 10, 2007

### noagname

I am just an 8th grader that likes physics
and I want to know if a car weighs 10 pounds then how much force is need to push it to a speed

8. Nov 10, 2007

### jdogg0075

I see. Well Im just a senior in high school that has loved physics since about 5th grade. Nice to meet you. Any who. Before we start about how much force there are some concepts that need to be understood. First is coefficient of static friction. Do not let it scare you.

Basically have you ever pushed a huge heavy box and it wont budge you would say well this is because there is too much friction. Right? But if you push hard enough it would move. This can be measured and recorded as what we call coeff. of static friction.

Now this value can be more than 1 or less than one, the lower the better. The formula for how much force is required to overcome friction is F= Normal Force * Coff. Friction

What is normal fore? You might know one of Newton's laws, for every force there is an equal and opposite force. Well when you sit in a chair the chair exerts the same force upwards and you stay still. So if you have a 10 pound car, the ground will exert 10 lbs of force upwards so your normal force is 10 lbs.

Force normal = Mass * 9.81 m/s^2. I got the 9.81 from the acceleration of gravity.

This is a lot to understand but you can always re-ask me for specific questions.

Then from that You can subtract your frictional force from pushing force then use
Force = mass * acceleration to find the acceleration of the object.

Also for further note use metric system, its better.

9. Nov 10, 2007

### noagname

nice to meet you to
http://en.wikipedia.org/wiki/Coefficient_of_friction
i have looked at this and i am confused
how do you calculate the coefficient of static friction
f= normal force * coff. Friction
f means force right
and last is well you last 2 or 3 sentences i don't understand
i can understand f=ma(we learned this in school)
but i think i am going back to my main question and that is
how do i calculate how much force it would take to push , move, speed up and more

10. Nov 10, 2007

### jdogg0075

By how to calculate the coefficient of static friction im guessing you want to calculate this.
The formula really should say Frictional force = coff. friction * normal force. Bacially coff. of friction has to be measured through experiments.

Let me give you an example of how to calculate acceleration form a situation.

Lets say for example i wanted to find the acceleration of a car that is 1000 kg when im applying a force of 2000 Newtons and the car has a coff. of .18 with the ground. First i wanna find the force i have to apply to overcome friction. To do this i use Frictional force = coff. * normal force.

Frictional force = .18 * (9.8*1000) Frictional force = 1764 N So basically to even get this car to move from rest i have to apply a force greater than 1764 N. Im applying 2000 N. If im pushing in one direction and the frictional force is opposing that. I would have to subtract the two so 2000-1764=236 N in my pushing direction.

Now using this force i can find the acceleration of the car with F= Mass * Acceleration
So i set it up 236 = 1000 * A
A= .236 m/s^2

Then there are formulas to go from there to find out velocity and other stuff. You can look around for that.

Hope this helps. : )

11. Nov 10, 2007

### noagname

thanks that was a lot of help

12. Nov 10, 2007

### noagname

what type of experiments

13. Nov 11, 2007

### jdogg0075

Well to find the coeff. of static friction you have to either know hey steel has a coeff. of .12 or somthing. Or you have conduct an experiment where you have a known mass on the surface. and like a pulley with a string conected to a weight. You keep adding weight until the body moves and then you can find the coff. of kinetic friction. This is all unnessecary things unless you really want to.

14. Nov 11, 2007

### noagname

ok
i haven't look online but is there some website that wood tell us what the coeff. of static friction was

15. Nov 11, 2007

### jdogg0075

Im sure there is somewhere. Id search the surface you are using. I personally dont know any.