丁香园AV

Inclined Kleenex ~30 Minutes

Description:A cup full of pennies will pull a kleenex box across, up, and down a board at different angles.

Objective: to investigate Forces and the Inclined Plane.

BC Science Content:

-effects of pushes/pulls on movement (grade K)

-types of forces (grade 2)

-properties of simple machines and their force effects (grade 5)

-effects of balanced and unbalanced forces in daily physical activities (grade 6)

Materials: A ***smooth board at least 50cm long, ***fullish klenex box, piece of string ~50s\cm long, Styrofoam cup, 2 pencil crayons, crayola marker, tape, ~50 pennies or marbles or other small metal objects

Doing it:

A1. The Styrofoam cup will be used to hold the pennies. With a sharp pencil punch two holes in the rim of the cup. Tie the string through the holes so the cup may be hung from the string. Attach the other end of the string to the kleenex box. The string should be attached near the bottom of the box so as when the string pulls on the box the box doesn't tip.
A2. Tape the marker to the end of the board. The marker will act as a pulley and keep the string from getting hung up on the corner of the board.

B1. First hold the board vertical, with the marker 'pulley' on the top. Hang the string over the marker, with the cup on one side and the box on the other. Put a handful of pennies in the cup so the box will stay still. Put a mark where the top of the bo is and on 5 cm higher. Now keep placing more in until the box starts to move upwards and moves past the mark. How many did you need? How much weight was it compared to the weight of the box?
B2. Now empty the pennies from the cup. Put the board on the desk with the 'pulley' end hanging off the edge. Place a marker under one end of the board so it is inclined, with the high end about 10cm off the table and at the edge of the desk. Put the box at the low end of the board with the cup hanging over the 'pulley'. Move the box so the front edge is 5cm below the edge of the board(not 5cm along the board but 5cm vertically. Now put pennies back into the cup, until the box slides to the top. Did you need more,fewer, or the same number of pennies to move the bo up compared to when the board was vertical? Why?
B3. Repeat B2 but use a stack of books instead of the marker. Try to get end of the board to be about 30 cm off the table. Again place the box so it is 5cm below the edge and repeat. Now how many pennies did you need? Did you need more,fewer, or the same number of pennies compared to when you used the marker? Compared to when the board was was vertical? Why?

Explanation: Explanation: When you add more pennies to the cup, gravity pulls more on the string, which pulls more on the box. The box will start to move once this pull is greater than the pull from the other side. The inclined plane allows more vertical movement with a lower pulling force. Comparing the parts B1, B2 and B3, we see that it will slide up to a certain height with fewest pennies in part B2 although it must slide further. This is the mechanical advantage of the inclined plane.