# Average force of friction help

1. May 29, 2007

### hockey45

1. The problem statement, all variables and given/known data
hi guys,
i am having trouble with this problem.
Calculate the average force of friction acting on a wood block as it is propelled along the floor by an elastic band ?

my solution and my ideas:
What does it mean by average froce of friction?
I first weighed the peice of wood to find its mass. i then used a newton scale and pulled the elastic band 60 cm and found the force of friction which was 8n. is this force applied(8n)?did i measure the force correctly of the elastic.?i have no idea where to go from here. is there any kinetic energy involved? do i use Ek=1/2 mv^2. any suggestions would be helpful. do i time the wodeen block after i let it go and find the velocity. i am sure it is uniform acceleration.
thank you.

2. May 30, 2007

### andrevdh

Welcome to PF Hockey.

If you did not accelerate the block while pulling it along the floor the reading on the scale should be the same as the frictional force opposing the motion of the block. We can deduce this from Newton's first law - no acceleration implies no resultant force (along the direction of the floor). This implies that the pulling force and frictional force was the same magnitude but acted in opposite directions.