|
Formal Lab Investigation |
| Title |
Estimating g using an Atwood machine |
| Category |
Newton's Laws |
| Purpose |
Determine if the gravity
constant really is 9.8 m/s/s. |
| Models |
Atwood equation: g = a(m1
+ m2)/(m1 - m2)
Kinematic equation: a = 2D/t2
|
| Overview |
After
attaching a pulley to a fixed point, we hook masses to the string
over the pulley. We then lower one of the masses until it touches
the floor. We finally release the lower mass and time the descent of
the higher mass, measuring this time and, through our equations,
determining the gravitational constant. |
| Safety
Issues |
Be careful
to regulate the descent of the higher mass so that it will occur
slowly and not crash to the floor. |
| Equipment
Limitations |
Possible
equipment limitations include friction between the pulley and the
string, which will slow the rate of descent of the mass. This
friction can be minimized by using a low-friction string or by
greasing the pulley. Air resistance is a source of error that cannot
be prevented, although its effects should not be substantial. The
size of the error can be estimated by evaluating the differences
between estimated values and the predicted gravitational constant. |