Newtonian Mechanics

Reactionary Roadbed

Radio controlled car moves one way while road moves the other.

What it shows:

We tell our students that, when a car drives down the road, the road and the Earth move in the opposite direction, albeit imperceptibly. This demonstration is a realization of that concept, made possible (and perceptible) by the fact that the road is not attached to the Earth.


Read more about Reactionary Roadbed
Reaction on Conveyor Track

What it shows:

A straightforward demonstration of Newton's 3rd law, that forces are interactions and thus come in pairs.

How it works:

Two people, each sitting (cross-legged) on their own board, position themselves in the center of the track facing each other. Upon pushing against each other with their hands, they glide apart down the length of the track. Repeat this with one person turned around — the other person pushes on his/her back instead of pushing against each other with their hands. The ensuing motion down the track is exactly the same as before.

... Read more about Reaction on Conveyor Track
Cavendish Experiment

Calculation of gravitational constant, with accompanying apparatus model.

What it shows

The gravitational attraction between lead spheres. The data from the demonstration can also be used to calculate the universal gravitational constant G.

gravitational attraction

Read more about Cavendish Experiment
Potential Well

Orbital motion simulated by ball rolling on wooden potential well.

What it shows:

Motion in a central potential is demonstrated by a ball rolling on a circular 1/r curved surface.

How it works:

The 1/r potential well simulates the gravitational potential surrounding a point mass; a ball bearing moving in this potential follows a parabolic or elliptical orbit depending upon its initial trajectory and velocity. As it loses energy due to friction, the orbit decays and the ball spirals towards the centre of the well. You could...

Read more about Potential Well
Reversible (Kater's) Pendulum

A physical pendulum with two adjustable knife edges for an accurate determination of "g".

What It Shows

An important application of the pendulum is the determination of the value of the acceleration due to gravity. By adding a second knife-edge pivot and two adjustable masses to the physical pendulum described in the Physical Pendulum demo, the value of g can be determined to 0.2% precision.

How It Works

Using a simple pendulum, the value of g can be determined by...

Read more about Reversible (Kater's) Pendulum
Feather and Dime

Falling in an evacuated tube at the same rate.

What it shows:

In the absence of air resistance all bodies, regardless of size or weight, fall with the same acceleration at the same point above the Earth. Here a feather and a dime (see Comments) fall under the influence of gravity in an environment where there is no air to mess things up.


Read more about Feather and Dime
Falling Faster than 'g'

What it shows:

Allow a board to rotate under the force of gravity and the free end will accelerate at a rate greater than g. Relation between angular acceleration and linear acceleration seems to give free-fall paradox.

How it works:

If a board, held in a vertical position with one end resting on the table, is allowed to...

Read more about Falling Faster than 'g'
Newton's Apple

Apple electronically released from platform; fall time given by special circuit and digital display.

What it shows:

This is a free-fall-from-rest experiment in which an apple (or any other object of comparable size) is dropped from the lecture hall ceiling into a catching bucket on the floor. By measuring the (1) distance and (2) duration of the fall, an accurate (± 0.022%) determination of the acceleration due to gravity can be made:


Read more about Newton's Apple
Double Atwood's Machine

Prediction of motion of masses in a more complex pulley/mass assembly.

double atwoods machine

What it shows:  This compund Atwood's Machine demonstrates an old and interesting problem. The two small weights on the right side are not of equal mass — one is 100 g and the other...

Read more about Double Atwood's Machine
Atwood's Machine

Combinations of weights suspended over pulley to show that asymmetry causes acceleration.

atwood's machine

Image on the left, of a lightweight plastic pulley with balanced 50 g brass weights, and on the right, the pulley in motion as the unbalanced weights accelerate.