Physics Photo of the Week
Galileo's Two Mass Drop. Video done by the Physics section taught
by Jason Zumstein.
by David Habib
The Physics Class at Warren Wilson each year repeats Galileo's famous
demonstration of proving that two drastically different objects (a
bowling ball and a golf ball) fall together with identical
accelerations. A physics student was very careful to let both
balls roll off his finger tips at the same time.
From the video it can be seen that the bowling ball and golf ball fall
at the same rate even though the bowling ball is 160 times more massive
than the golf ball. The velocity of both balls also increase as the
balls fall. Rate of change in velocity is known as acceleration and is
expressed in Newton’s second law by the formula:
accel = force/mass.
This states that an object’s acceleration is proportional to the force
on the object and inversely proportional to the object's mass. However,
if Newton’s second law is true, why then do objects with different
masses accelerate towards the earth at the same rate? The force
of gravity on the bowling ball is 160 times greater than the force of
gravity on the golf ball. To answer why acceleration due to
gravity is the same for all objects we simply use Newton's second law
of the above formula.
In the formula, both the force and the mass are 160 times greater for
the bowling ball. When calculating the acceleration from the
ratio of force to mass, the 160 factor cancels out both in the
numerator and denominator. Therefore the acceleration due to
gravity is independent of the mass of the object in question.
When air resistance is ignored all objects at the same altitude and
latitude will fall at the same rate.
Photo of the
published weekly during the academic year on Fridays by the Warren
Wilson College Physics
Department. These photos feature interesting phenomena in
the world around us. Students, faculty, and others are invited to
submit digital (or film) photographs for publication and
explanation. Atmospheric phenomena are especially welcome.
Please send any photos to firstname.lastname@example.org.
All photos and discussions are copyright by Donald
Collins or by the person credited for the photo and/or
discussion. These photos and discussions may be used for private
individual use or educational use. Any commercial use without
written permission of the photoprovider is forbidden.
see the Physics Photo
the Week Archive.
Observers are invited to submit
digital photos to: