Video demonstration experiments show the laws and concepts in action.
In the first part of the video, we will be demonstrating Newton’s Laws. The Air Puck ejects a stream of air that allows it to float and move with minimal friction. When you launch the puck, without the stream of air, it slows down and eventually comes to a complete stop due to friction. When you launch the puck with the stream of air which greatly reduces the force of friction, it will stay in motion.
Inertia: Block and Hammer
If you work in a workshop, you may have replaced a hammer handle before. We have a similar contraption, with a heavy block of wood and a piece of PVC tubing. When the top of the tube is stricken by the mallet, the block of wood stays in place due to its inertia and the PVC tube slowly ‘falls’ through the block. This causes the block of wood to seemingly ride up the tube.
Phone Book Friction
With no readily available phone books, we decided to use some old lab books instead. The pages of the two books are interleaved. The coefficient of friction between the pages remains the same throughout the experiment, but when you try to pull the books apart, the pages in the middle get squished together– this increases the normal force between them, thus increasing the friction as well. The harder you pull, the larger the friction gets!
Hooke’s Law: Different Spring Constants
Our Hooke’s Law demonstration uses three springs with different spring constants and three equal 1kg masses. Once we hang the masses on the three springs, you will see that each spring is stretched different amounts even though they are experiencing the same amount of force. This is because for the same pulling force the amount of stretching is inversely proportional to the spring constant. When we set each mass to oscillate, the period of oscillation is inversely proportional to the square root of the spring constant, assuming simple harmonic motion. The experiment confirms that the springs with higher spring constant have shorter periods of oscillations.
Kinetic vs Static Friction
Our apparatus consists of a wooden block with a string attached, a force sensor, and an iPad that receives the data from the sensor. The top left contains two diagrams, one is a graph of force vs time and the other just reads the force at that moment. We attach the force sensor to the other end of the string and use it to pull on the wooden block. We slowly increase our pull on the block until it starts to move. The graph will indicate a sudden dip in the applied force. This is because we initially have to overcome the static friction, which is what keeps the block from being pulled. Once we apply a sufficient amount of force, the block will be in motion and thus the opposing force will now be the kinetic friction. Static friction tends to be larger than the kinetic friction, resulting in the dip we see in the graph. The experiment is then repeated but with additional weight on the wooden block. This will increase the frictional force, requiring us to apply more force to overcome to set the block in motion.
Smash Your Hand
Here we have a heavy block of metal, due to its large mass it also has a lot of inertia. Inertia is a property of an object that resists any change in its motion. When we strike the block with a hammer, the block will barely move, if at all, due to its high inertia. This allows the presenter to place the block on his hand and strike at the block without getting hurt.
Inertia: Tablecloth and Dishes
This is a classic example of inertia. Here we have some dishes on top of a tablecloth. If we pull on the tablecloth slowly, then dishes move with the tablecloth due to friction. If we pull the tablecloth quickly, then the dishes will stay in place due to their inertia.
Inertia with Soda Cans
When the cloth is pulled slowly, the force of friction between the soda cans and cloth has enough time to overcome the soda cans' inertia and give them a nonzero momentum, causing the cans to fall. When the cloth is pulled quickly the impulse due the force of friction is too small, and soda cans remain at rest.
Bed of Nails
Here we have three different beds of nails of equal areas, all of them with different amounts of nails. The first bed of nails has the most nails out of the three. When an object (i.e a balloon) is pressed against it, the force will be distributed evenly across all of the nails, resulting in minimal pressure applied by the nails. Thus the balloon does not pop. A similar result is achieved with the second bed of nails. The third bed of nails has the least amount of nails. When the balloon is pressed against it, it almost immediately pops due to each nail applying significantly greater pressure than the two previous examples.