Toys and Physics - Mechanics

6.8 Soap bubbles

What happens
Bubbles can be blown using the special loop or funnel. They are spherical and show wonderful colours.

Theory and teaching notes
There is a vast amount of useful physics in soap bubbles.
A large film on four rods can be made to oscillate like a drum skin showing simple harmonic motion.

Application areas: surface tension, air pressure, electrostatics, interference, oscillations

6.9 Cartesian diver

What happens
When blow into the tube the diver rises towards the surface. When you suck the diver sinks.

Theory and teaching notes
This is rather like the principle of the submarine. Blowing into the tube decreases the average density of the diver and so increases its buoyancy. Sucking the air out does the reverse.

6.10 Dipping bird

What happens
When the birds head is wetted by immersing it in the water it sways backwards and forwards, dipping its head in the water.

Theory and teaching notes
.As the liquid inside its body evaporates it forces liquid up the neck altering the balance of the bird which then dips its head into the water. Try doing the experiement with alcohol!
If the head is not wetted then a very instructive version of the experiment occurs. The bird tends not to drink but placing a saucer of hot water beneath its bottom will heat up the liquid sufficiently increase the rate of evaporation and make it start rocking. Energy is provided by the hot water – you don't get something for nothing

6.11 Falling pile of paper

What happens
When you drop the paper all the sheets fall together. None of them 'float' to the ground.

Theory and teaching notes

6.12 Helium filled balloon

What happens
The balloon moves in the opposite direction that you would expect when the car accelerates or brakes. When the car brakes the balloon moves backwards and when the car accelerates it moves forwards.

Theory and teaching notes
This happens because the average density of helium within the balloon and the balloon fabric is less than that of the surrounding air.

6.13 Dimensional animals

What happens
The set of farm animals can be use to demonstrate the idea of dimensions and dimensional analysis.

Theory and teaching notes
You cannot add mass to length or time. The dimensions on either side of an equation must balance.

6.14 Energy ball

What happens
When you drop the ball onto the floor the light inside it flashes for a few seconds.

Theory and teaching notes
The potential energy of the ball is converted to kinetic energy as it falls and this operates a trigger switch within the ball when it hits the ground.
A useful demonstration of energy conservation.

6.15 Bouncing ball bearings

What happens
The ball bearings fall from a chute at the top of the tower onto the first of the rubber trampolines. They bounce off onto the second and then the third trampolines and then into the collecting box.

Theory and teaching notes
The angle of the chute and the height from which they fall is just right for the parabolic path of the ball bearings to hit the trampoline so that the rebound parabola takes them on to the next trampoline and so on.

I saw this wonderful toy that shows projectile motion being demonstrated by Jim Jardine at Lancaster University. Unfortunately I believe it is no longer available but it is well worth trying to make one yourself!

6.16 Slinky spring

What happens
The slinky is held by one end and allowed to dangle vertically. The upper coils are widely spaced while the lower coils are close together. The question is – what happens to the lowest coil at the moment the slinky is dropped.

Theory and teaching notes

6.17 Floating paper tube

What happens
You need an isosceles right angled triangle of paper. The long edge is then bent over twice – each bend being about 0.3 cm wide. This is then bent round in a circle to join the two pointed ends forming a shape rather like a bishop's mitre. The end is then bent upwards to give he shape shown in the photograph. If you hold the paper near to the bent up tail and then let it go it will float across the room covering a distance of many metres.

There are many possibilities for investigating the range with different types of paper, size of bend and angle and size of the "tail".

Many thanks to Ian Milne from New Zealand for this idea.

6.18 Newton's cradle

What happens
This is an essential "toy" for any Physics department. The movement of the static balls after being hit by one or two or even three others is impressive.


Teaching notes
Try investigating what happens when a small piece of Velcro is stuck to the colliding surfaces of two of the balls.
A wonderful example of the conservation of momentum in elastic and inelastic collisions.

6.19 Smiley pop ups and projectile motion

In his book 'Experiments in Physics' Colin Siddons suggested these of small 'pop-up' toys to study projectile motion. The toys, called Smiley Pop Ups, are very cheap (about 35p in 2005) and introduce a little bit of fun into the experiment.

You squash the toy onto the bench and then the rubber sucker slowly comes off and the toy launches itself into the air.

Theory and teaching notes
Since the same spring is used each time the launching force should be the same. This means that both vertical motion and motion at an angle to the vertical can be investigated. For the angles motion I have used tilted runways or even tilted the lab tables where this has been possible.

Fix a pin through a piece of sellotape stuck to the ramp on put a piece of rough paper on the slope will stop the toys slipping down the slope.

These toys can form the basis of an investigation at GCSE or A level.