Pushes and Pulls on the Tide-Pool Trail

Testing a Trail Cart

At a beach visitor center, students study a small model of a supply cart. Rangers use full-size carts to carry supplies along a dry path near the tide pools. The students keep their model indoors, away from the water and the animals.

A force is a push or a pull. Forces can act on an object in opposite directions. Equal forces in opposite directions are called balanced forces. When the forces in opposite directions are unequal, they are called unbalanced forces. The students want to find out what happens to their cart in each case.

They place the same cart at the same starting mark on a level board. Two short cords let them pull gently in opposite directions. Before every trial, they make sure the cart is at rest. They change the amounts of force acting to the left and right. They watch the cart for two seconds and record whether it moves and in which direction.

Their teacher helps compare all the forces acting to the left and right, including any rubbing from the board. In their notes, weak always means the same smaller amount of force. Strong always means the same larger amount. The directions describe the cart as seen from above.