Physics 121 Weeks 4 & 5
Static equilibrium is always easiest to talk about when you have an example. This pulley/ropes system provides a large visual which you and your students can analyze as you discuss or introduce how to solve a statics problem!
A spring balance is attached to a ring stand, and then a string is draped over the hook. Use the string tension on both sides of the pulley and compare it to the reading on the spring scale as you work through this statics problem.
A cart is set up on an inclined plane, and attached to two strings on pulleys with masses at the ends to keep it from moving. This demonstration allows students to calculate a theoretical statics problem, and then verify their results with an exciting reveal.
This object negates surface friction to allow you to demonstrate how a constant force will always result in uniform acceleration, and that an object will travel at constant velocity when no net force acts on it. If only this device was around when Aristotle was thinking about constant forces.
A ball is rolled down an inclined plane on wheels. When the ramp is held in place, the system behaves normally. When the ramp is allowed to roll, the ramp is pushed backwards demonstrating Newton’s Third Law.
With the fan turned on, the cart accelerates uniformly. Ask students "what will happen when the sail is held in front of the cart?" and "when it is attached to the cart?" A further conundrum can be added by putting a small folder in between the attached said and fan, causing the cart to again accelerate.
Place a block on an inclined plane. The angle can be varied to demonstrate the difference between kinetic and static frictions, as well as to verify a critical angle that you and your students can derive in class or for homework!
A block is set up on the desk, connected to a rubber band a force sensor. Gently pull the block while collecting data in logger pro. You should generate a classic friction graph showing a linear relationship until the max static friction is achieved and the block begins to move. Relate this to coefficients of friction.
Using a spring scale, you can show how much force it takes to get the box to move, and how much force it takes to move the box at a constant velocity. This works best on a rough tabletop with at least 1kg or more in the box.
Use eggshell foam to model a microscopic view of a rough surface. Both pieces of foam are dragged across each other to show how microscopic inconsistencies catch on each other, and that is what causes friction. Soda cans can then be added between the foam as a model of lubricants.
A plastic ball is placed on a small plastic sheet. Use the metal bar to quickly snap the sheet out from under the ball just like ripping a table cloth out from under some dishes. This can also be shown with a plastic card and a coin. Flick the card from under the coin, and letting it drop.
Can you get the marker into the jug by touching only the hoop? Challenge your students to complete the task first for some good laughs in the classroom. Rapidly PULL the hoop away by grabbing it along its inner wall, pulling outwards (think of a karate chop hitting the inside of the hoop NOT the outside).
Inertia can be a challenging topic, and this demo provides a tangible and visual example to help students grasp the concept. A rapid pull on the rod breaks the lower string, while a slow pull breaks the upper string. Paradoxical at first glance, Inertia is the answer for this one!
Gently swing the RUBBER MALLET into the side of each rock. The foam one will undergo a greater acceleration.