# Demo Videos: Basic Mechanics

Physics demonstrations of the key concepts of mechanics. View demos illustrating kinematics of linear and circular motion, force  and Newton’s Laws, torque, center of mass, center of gravity, and rotational inertia.

For other videos from our demonstration collection, please visit Physics Demo Videos. You may also wish to view our Video Lecture Series for short tutorials on topics from first year physics.

[Note: if you get an error message on playing a video, try clearing your browser’s cache and cookies, or try viewing in an incognito window.]

## Constant Acceleration

Simultaneous fall:: Each ball is an example of a simple type of motion; one ball falls straight down and the other ball is launched in a parabola.
Trash can toss: The center of mass moves in simple projectile motion as the trash can tumbles through the air.
Monkey-hunter. The falling target experiences the same vertical acceleration as a ball launched from a cannon aimed at it. They will hit if released at the same time. (Hint: try watching in slow motion using the video settings. Version 1
Version 2
Version 3
Falling chimney, with a twist. The acceleration of the stick is more than the acceleration of ball. Thus, the stick’s cup will be in place to catch the ball even though both are released at the same time. Take 2.

## Circular motion

Loop-de-loop. When released high enough on the longer part of the track, the ball will be accelerated enough to loop the loop.
Merry-go-round.  People in a rotating reference frame experience pseudo-forces such as centrifugal force and Coriolis force.
External observer taek 1 and external observer take 2. Why is it so hard to toss the ball to each other?
Internal observer. Watch the ball curve dramatically.
Roller coaster. The car experiences centripetal acceleration while traveling the loop.
Rotating bucket. The bucket (and water contained therein) experiences centripetal acceleration when swung in a circle. Why does the water stay in the bucket?
Rocket Cart. The force of the escaping gas from the fire extinguisher accelerates the person on the cart.

## Force and Newton’s Laws

Springs and Hooke’s Law: A spring will be stretched a distance proportional to the amount of mass that is added to the spring. Light mass. Medium mass, Heavy mass.
Tablecloth pull, Newton’s First Law: The objects on the table tend to stay at rest due to their inertia.
Toilet paper. Newton’s First and Second Laws. If you pull the toilet paper slowly, little force is required to accelerate the paper and you can pull off lots of paper. However, much force is required to accelerate the roll quickly, ripping the paper.

## Torque, Rotation, Center of Mass, Center of Gravity, Rotational Inertia

Fourteen hook bar: Different combinations of mass and distance from pivot are required to balance the torques on the stick.
Odd-shaped bar. Note that only the mass and the horizontal distance from the pivot point are important.
Long wrench vs. short wrench. The instructor can loosen a bolt more easily with a longer wrench.
Inertia rods. These rods weigh the same, but due to the distribution of the mass, one is harder to rotate than the other.
Balancing  bird: The bird balances easily on the instructor’s fingertip. What can you say about the position of the center of mass of the bird?
Horse and rider. The horse and rider balance easily on the horse’s hind legs. Where is the center of mass of the horse-rider-weight system?
Double cone and wedge trick.  Look carefully; the center of mass of the cone is actually rolling down hill. An optical illusion makes it look like it is rolling up.
Feeble-minded disk. Why does the disk roll uphill? Hint: the center of mass of the disk is not at its center. Where must it be?