Unknown Bricks, 1F10.25

Topic and Concept:

• Newton's First Law, [:Newtons1STLaw: 1F20. Measuring Inertia]

Location:

• Cabinet: [:MechanicsCabinet:Mechanic (ME)]

• Bay: [:MechanicsCabinetBayB5:(B5)]

• Shelf: #1

attachment:UnknownBricks-01-400.jpg

Abstract:

A lead brick and a wooden block(balsa wood) of the same dimensions are both wrapped in aluminum foil to look identical. Each block is then hit with a hammer. Then toss the wooden block to a student.

Important Setup Notes:

• N/A

Setup and Procedure:

1. Place the two blocks on the table, and tell the audience which two materials are concealed before their eyes.
2. Tell the audience you will do your best to apply equivalent forces via the hammer to each block then do it.
3. The lead block will barely move it at all while the wood block will go sliding across the table.
4. Ask the audience which block they think is which.
5. (Optional) Toss the light, wood block to a student. If they understand physics well enough, they shouldn't freak out.

Cautions, Warnings, or Safety Concerns:

• The lead block is heavy. Don't drop it - it could cause serious damage to the floor, table, or your foot.

Discussion:

The lead block is much more dense than the wood block. Therefore, since the two blocks have the same dimensions, the lead block will be much heavier than the wood block. In other words, the lead block has much more inertia than the wood block. When hitting each block with the hammer, due to the large mass of the lead block, it will barely move and due to the comparatively small mass of the wood block, it will go sliding across the table. These ideas are quantified in Newton's second law: F = m*a, the larger the mass of the object, the less acceleration it will obtain by a given force.

Videos:

• [https://www.youtube.com/user/LectureDemostrations/videos?view=1 Lecture Demonstration's Youtube Channel]

References:

• N/A

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