Consider inviting students to make predictions about how the shape of the ellipse will change in response to changing the foci in different ways. This can be related to a variety of mathematical and astronomical phenomena.

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.

Place the lead brick gently on your fingers and strike the lead brick sharply with the hammer. The inertia of the lead brick prevents damage to your fingers.

Engagement Suggestion

Engagement Suggestion:

Background:

Newton’s First Law of Motion states that an object’s velocity is constant unless there is a net force acting on it. What this means is that if an object is not moving (at rest), it will not start moving until there is a force pushing or pulling on it. If an object is moving at a constant speed and direction, it will keep going with that same speed and direction unless a force pushes or pulls on it to change that. When the pen is sitting on top of the hoop, the force of gravity is pulling it down, but the normal force of the hoop is exactly equal to the gravitational force and holds it up. If another force suddenly affects the pen (such as if you walk up and tap on its side, or jiggle the hoop up and down), that force could cause it to move, and probably fall.

But if the hoop is snatched sideways quickly and smoothly, it does not give any force to the pen. Now the only force acting on the pen is gravity, and the pen falls straight down into the bottle.

CAUTION: Be sure that the hose fitting is securely attached to the tube and that the plastic shield is in place before firing. The shield should be latched in place, with no debris blocking its edge from meeting the baseplate

Engagement Suggestions

• • Before using, encourage your students to predict what will happen to the pencil.
• • For advanced students, discuss the energy involved in the problem and where the kinetic energy of the pencil went after the collision.

Background

This demonstration can be presented in multiple ways. It has been offered classically as an illustration of the principle of inertia – the pencil is in motion at a high velocity, and continues in motion despite the intervening wood until arrested by a greater force. Alternatively, consider the high velocity and high momentum of the pencil. The abrupt deceleration at the plywood means a high impulse. The pointed pencil has a very small cross-sectional area, resulting in force applied over a small area leading to a high momentary pressure.

Linked below is a slow-motion video of the collision, shot at 600 frames per second. A fun class activity could be to use the video to measure the motion of the pencil and estimate its momentum and kinetic energy, based on what you see in the video and by measuring typical lengths and masses for wooden pencils.

Background

Turning the crank causes the elastic rings to rotate about the vertical axis. The rotation mechanism here uses the mechanical advantage of a large cranked wheel driving a smaller pulley to give the rotating rings a very high angular velocity.

Engagement Suggestion

Background

This effect is seen in astronomy and geography, as rotating planets, stars, and other bodies take on similarly oblate spheroidal forms.

Please take care when using this device, especially when accelerating. You can gain a significant increase in rotational speed, so hold on! And it is best not to have a person push the chair around very much, as it is very easy to hit them with a weight by accident.

Engagement Suggestions

Background

To show this in a different way, a single user with a single weight can move themself in a circle by swinging their arm wide holding the weight from front to back, then drawing it inwards before extending their arm forwards again and repeating the motion. This is essentially a rotational analogue of pumping a swing.

Sit on the chair (chair not rotating) with the wheel spinning and its axis oriented vertically. Reverse the angular momentum vector of the wheel by inverting the wheel, thus causing the entire chair to rotate in the original direction of the wheel rotation. Returning the wheel to its initial orientation causes the chair to cease its rotation.

Because the friction in the bearing of the rotating chair is very low, several cycles of this procedure can usually be completed before the system loses its energy and stops.

Engagement Suggestions

Invite students to predict how changing the ball’s starting velocity (in magnitude or direction) will affect its path. This is a good opportunity for one or more student volunteers to participate.

Background

The surface of this “potential well" is shaped so as to model an inverse square gravitational force. When a ball enters the well enters the well, it is attracted to the center; if it has no initial velocity, it will fall directly to the center. But if it enters with some velocity tangential to the center, it will fall into an elliptical orbit that gradually decays to the center as the ball rolls around the well.

When you roll the ball across the surface, you use some initial force to start it moving. Once it is rolling on its own, though, the only forces acting on it are the force of gravity, pulling downwards, and the normal force and frictional force of the surface holding it up. So the ball accelerates as it rolls down the surface, exchanging potential energy for kinetic energy, until it falls into the hole.