Negative Forces?

[rockinaway]

Is it possible to have negative forces?

 

For example I have a question:

 

The impact between the head and the dashboard lasts 0.008s

 

Calculate the impact force between the head and the dashboard.

 

So I do F = (mv-mu)/t

 

= -112/0.008

 

Now I get the answer -14,000N...

 

In am exam would I write -14,000N or just 14,000N?

[ydoaPs]

It depends how you set up your frame of reference. Remember that force is a vector, so it has both a magnitude and a direction.

[JaKiri]

A negative force is just a force in the opposite direction. In your example, you've got the positive force direction in the diretion of travel - ie one that causes the head to speed up.

[Fred56]

My 'simple' explanation of how there is no such thing as a negative 'force' is how electrons and protons cancel each other's charge, but they don't disappear or annihilate (even though the charge vector is zero, algebraically speaking).

Also, two things traveling in opposite directions don't cancel each other's momentum, which is conserved instead (it 'goes' somewhere)

[ydoaPs]

My 'simple' explanation of how there is no such thing as a negative 'force' is how electrons and protons cancel each other's charge, but they don't disappear or annihilate (even though the charge vector is zero, algebraically speaking).

 

Why would they annihilate if the forces cancel?

[Fred56]

Why are you asking?

[ydoaPs]

Because it doesn't seem like you've proved anything.

[Fred56]

OK -it doesn't seem like you're asking anything.