This practical consists of a series of demonstrations which show the principles of simple harmonic motion (SHM). SHM is the motion of an object which is periodic and which is not driven or damped. In essence, the type of movement produced by a swinging pendulum is typical of SHM.

All harmonic oscillations have fixed principles:

• each complete oscillation takes the same time.
• a force returns the system to its equilibrium position when displaced.
• an inertia factor makes the system overshoot its equilibrium position when in motion.
• If the acceleration of a body is directly proportional to its distance from a fixed point, and is always directed towards that point, the motion is simple harmonic.

Four demonstration examples are included here which are routinely conducted in school science to prove these principles.

Traditional pendulum

Equipment required:

• Tall stand and clamp
• 'G' clamps
• string
• small mass
• timer

This comprises a tall retort stand which is clamped firmly to the desk using 'G' clamps. From the stand clamp is tied a length of string and at the end of the string is fixed a mass. This mass does not have to be large, a 100g slotted mass is perfect for this.

The mass is set in motion by lifting it slightly while the string remains taught and released. Students use the timer to record the length of time taken for a complete period of oscillation.

Trolley Displacement

Equipment required:

• standard physics trolley with two metal bars or anchor points
• two large springs
• two short stands and clamps
• 'G' clamps
• timer

This demonstration comprises a dynamics trolley and two springs. A spring is attached to each end of the trolley and the other ends attached to a clamp and stand which is firmly secured to a desk using 'G' clamps. The trolley should be equally distanced from the stands and the springs should be extended slightly so that they both exert a small pull on the trolley. If the trolley is set in motion by pushing it to one side, SHM will occur as it oscillates back and forth, slowing only because of friction. Students use the timer to measure theperiod of oscillation.

Spring and Mass

Equipment required:

• spring
• clamp and tall stand
• 'G' clamp
• small mass
• timer

This demonstration involves clamping a spring at the top of a tall stand. The stand needs to be firmly attached to the desk using a 'G' clamp. The free end of the spring is attached to a small mass. A 100g slotted mass is perfect for this. To set the mass in motion, pull down on it slightly to allow the spring to pull it back up, producing SHM. Again, students can measure the amount to fime taken for a single oscillation.

Rolling ball

Equipment required:

• large watchglass
• marble

This simple demonstration involves setting a marble in motion within an upturned watchglass. As the ball is released, the ball travels in an oscillation manner until it comes to rest.