Determine the coefficient of static friction between wood and three different materials.
Preparation:
You will need to gather the following materials:
2 wood blocks
Pulley
Roll of pennies
Small Basket
Procedure:
The wood blocks I used measured 3.5"x 1.5"x 1.5", however you can use whatever size
you have. My pulley was the spool for the thread on a nail. My basket was the bottom cut
from a Pepsi can.
Determine the mass of the wood blocks and basket relative to the mass of a penny (my
blocks were about 22 p. and my basket about 2 p.). Connect one block to the basket with
about two feet of thread. Fix the pulley so that it is just past the lip of a table. Place the
block on the table with the thread over the pulley and the basket hanging (see fig. 4.23 on
page 105 of your text).
Place pennies, one at a time, in the basket until the block begins to move. The sum of the
relative mass of the basket and the number of pennies will be $m_h$, the hanging mass. The
force needed to overcome friction between the block and the table will therefore be $m_hg$.
Let $m_b$ be the relative mass of the block. The normal force between the block and the
table will be $m_bg$. Now calculate $\mu_s$, the coefficient of static friction, between the block
and table ($m_hg = m_bg \times \mu_s$)
Repeat this with the second block atop the first. Are the values of $\mu_s$ the same? Note:
friction in the pulley created a problem in my case that was overcome by some olive oil.
Repeat this experiment with the block/s resting on two other surfaces (i.e. glass, metal
etc...). You should have three runs total, each on a different surface done with a single
and then double block.
