1. The Atwood Machine
Formal Lab Report

2. Atwood’s Machine
The purpose of this laboratory exercise is to investigate the validity of Newton’s Second Law of Motion. You will use a single pulley apparatus as shown. This apparatus is commonly referred to as an “Atwood Machine”. The Atwood Machine allows one object to hoist another object using only gravity.

3. Atwood’s Machine
To determine the tension in the string (FT), we have to draw a free-body diagram FT FT M2 M1
Fgm1
Fgm2

4. Making Sense Of It! Fm2 = m2a = m2 g – FT Eqn 1 and
How can we simplify this?

5. Here’s How!
We can determine the Fg’s because we know the masses involved and g is always 9.8 m/s2.
The problem is FT  we don’t know what it is and we can not calculate it!?!
Lets get rid of it!  Make a substitution

6. Substitute for FT If m2a = m2 g – FT, then FT = m2 g – m2a
Substitute m2 g – m2a in for FT in Eqn 2.
And get m1a = -m1 g + m2 g – m2a

7. Simplify m1a = -m1 g + m2 g – m2a + m2a + m2a m1a + m2a = -m1 g + m2 g
Factor out the a’s and g’s
a(m1 + m2) = g(-m1 + m2)

8. Solve for the acceleration
a (m1 + m2) = g(-m1 + m2)
(m1 + m2) (m1 + m2)

9. Solve for the acceleration
a = g (-m1 + m2)
(m1 + m2) OR
a = g (m2 - m1)

10. Therefore a = g (m2 - m1) (m1 + m2)
Therefore we can compare our calculation from the above equation to the actual acceleration from our graph to determine the validity of Newton’s 2nd Law!