To observe the displacement of an object at constant acceleration, a cart is sent down an inclined air track, with flags or sticky notes marking positions on the track. These positions correspond to the increasing distances traveled over equal time intervals. A metronome provides these time intervals. When set up properly, the cart should pass over each flag or sticky note on each metronome beep.
The Galileo ramp demonstration allows students to observe acceleration due to gravity, via the motion of a cart on an inclined air track, as is predicted from the kinematics equation (with both an initial velocity and displacement of 0):
x = at2
- Air track
- Blower (air supply) and air hose
- Metronome with audio cable
- Air track cart with ping pong ball
- Marked sticky notes or marked flags
- Bumper with rubber band
- 100 gram weight labeled “Galileo Track”
All parts are located in room 202, the lecture prep demonstration room. The air track is above shelves G and H. This specific air track is needed (instead of the ones in room 215) because it has black markings on its scale. The blower and air hose are on the floor beneath
the left side of shelf E1. The metronome and cable are located to the left of the center of shelf P3. The air track cart (which should have an orange ping pong ball on one of its sides to make viewing the cart’s motion easier), marked sticky notes and flags, and the bumper with the rubber band are in a green cardboard box, on shelf K1. The 100 gram weight is on shelf J2 and has the label “Galileo Track” in orange. The thickness of the weight, not the mass, is important for the demonstration.
Place the air track on a flat surface and insert the air hose into the side of the air track. The other end of the air hose should be in the back of the blower. To level the track, turn on the blower using the red switch (a setting of 3 should work, but adjust as needed) and place the air cart from the green box on the track. Adjust the legs of the air track so that the cart does not move forward or backward. Once the air track is leveled, turn the blower off. Place the 100 gram weight underneath the single leg of the air track. Put the bumper on the opposite end of the track. If the rubber band is worn out, check the green box for other bumpers. If none are available, there are replacement rubber bands in the cabinets of room 215.
Take the sticky notes (or, if you prefer, the numbered flags in the green box) and stick them onto the scale of the air track cart so that the black mark of the scale lines up with the black mark on the sticky note (or the base of the flag). Scotch tape comes in handy for this. The first note or flag, labeled “0”, should match up with 192 cm, and the last, labeled “25” should match up with 17 cm. There should be a total of 6 notes or flags.
Adjust the metronome tempo to 40 beats per minute. The audio cable is available for projecting the metronome beep in a classroom. Plug one end of the cable into the metronome, and the other into the classroom’s laptop sound jack, which is located in the front of most classrooms. In room 205, the laptop sound jack is broken, so use the sound system, both the primary and secondary sound jacks will work.
How it works
Using your hand, hold the cart at the top of the tilted air track (with the blower on), right above the sticky note or flag marked “0”. As the metronome is beeping, release the cart on one of the metronome beeps. With each beep, the cart will pass over one of the flags or the sticky notes. The orange ping pong ball on the cart is meant to make this easier for students to view from their seats.