Table of Mechanics Demonstration List of Mechanics Equipment & Supplies Lecture Demonstrations

# Push Me, Pull Me Cart 1H10.10

Topic and Concept:

Location:

Abstract:

Two people on roller carts or roller chairs each hold on to opposite ends of a wooden rod. They each push or pull on the rod causing a reaction on the opposite person.

 Equipment Location ID Number Red & Blue Roller Carts ME, Bay A4, Shelf T Chairs Room 2103, First Row Wooden Rod

Important Setup Notes:

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Setup and Procedure:

1. Place a chair on each cart such that each chair is in the most stable position.
2. Have a volunteer sit on each cart.
3. Have the volunteers hold on to each end so that they are opposing each other.
4. Ask the volunteers to push and/or pull on their respective end of the stick.

Cautions, Warnings, or Safety Concerns:

• Make sure the volunteers on are careful while on the carts. The chairs are not very stable.

Discussion:

When one person pushes or pulls on the rod, the rod applies the same force in equal magnitude but opposite in direction as per Newton's third law. This force is then applied to the other person by the rod. The person then exerts an equal and opposite force on the rod which effectively cancels the initially applied force (neglecting friction). The net result of this push/pull motion is zero net motion of the volunteer-cart-stick system (this is not completely true since there is some friction in the axles and bearings of the cart wheels), ie. momentum is conserved. The system starts with zero momentum thus when one person pushes on the rod, the other person moves in response to the force. However, the pusher must move in the opposite direction at a speed dependent on their respective mass to keep the total momentum zero.

Videos:

References:

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