Place the box on the inclined plane with a mass in it, and let the students see it slide down the slope. Challenge them to predict the mass that is needed to hang off the end in order to keep the box stationary.

Given an angle of inclination a of the inclined plane, this apparatus demonstrates that the mass m required to hold a cart of mass M at equilibrium on the inclined plane is given by:

Note that this demonstration and demonstrations B2-21 and B2-22 use many of the same components.

Engagement Suggestion:

Background:

The ball on the straight track retains essentially the same velocity and the same kinetic energy throughout the length of its run, the kinetic energy from the spring. The ball on the dipped track, however, has a more complex path. When it goes downhill, it gains kinetic energy from gravitational potential, accelerating it. It travels along the lower section of track with this increased kinetic energy, and thus greater velocity. The ball then goes uphill again, losing that additional kinetic energy – it has returned to the same height, so the principle of conservation of energy dictates that it must return to the same gravitational potential as before, giving up kinetic energy equal to what it gained. It now has only the same kinetic energy it started with, as imparted by the spring. So its velocity is now the same as its starting velocity, and the same as the velocity of the other ball.

However, during the time it was on the lowered section track, it had greater kinetic energy and greater velocity, so it traveled that distance faster than the ball on the straight track. And thus the ball on the dipped track reaches the end first, but with the same final velocity and the same final kinetic energy.

The launcher is aimed at the monkey and shot. As the projectile leaves the muzzle of the gun it breaks a circuit producing the magnetic field which holds the monkey in place. The monkey then begins to fall at the same time the projectile is fired directly at the monkey. Due to independence of horizontal and vertical components of motion, the projectile will strike the monkey.

Note that the angle can be varied to show different horizontal and vertical components.

Equal masses M of 200 grams are hung on the ends of a light string passing over a light, frictionless pulley. When an additional mass of 100g is hung on one end, the resulting acceleration can be measured by timing the motion of either mass over a distance S between two points. The acceleration of gravity g can then be calculated: g = a (2M + m)/m, where a is the acceleration of the system: a = 2S /t^2.

Click here to go to a simulation of this device by Erik Neumann.