Fast and Easy Science Fair Projects: Work = Force x Distance Essay
The wedge, a simple machine
Purpose: Show the relationship between the distance a wedge is moved forward and the height an object sitting on top of the wedge is raised.
Overview: A “wedge” is one of those “simple machines” we talked about. A wedge is an object in the shape of a triangle. A doorstep and the metal head of an axe are exampled of wedges.
When an axe or chopping maul is used to split firewood, the worker swings the tool over a large distance to strike the wood with great force. That force is turned into the small distance covered by the wedge, as the axe moves down into the wood to split it. In Science, “work” is a measurement equal to “force times “distance.”
When a force is applied to a wedge, the force moves the wedge forward, but it also moves anything resting on top of the wedge into an upward direction (at a 90-degree angle to the forward movement of the wedge).
A wedge can be used to lift very heavy objects a short distance. House movers sometimes use wedges between the sill plate and the foundation to raise a house up so steel girders can be slid under it.
Hypothesis: Using a wedge increases the amount of force in a perpendicular direction, but we pay for it in a decrease in distance.
- A wide strip of thick cardboard, about 12 inches (30 cm) long
- Two rulers
- Small, light cardboard box (shoebox or similar size)
- 1 or more heavy books
Procedure: Draw a right triangle on a thick piece of cardboard. Make the triangle about 2 inches (5 cm) tall by about 12 inches (30 cm) in length. The hypotenuse of the triangle will form a long, gently sloping ramp. Use scissors to cut the triangle out.
Place a small, light box on a table. A shoebox would be perfect. At one end of the box, stack one or two heavy books. That will keep the box from sliding.
At the other end, place your cutout wedge so that its pointed tip just slips under the box. Lay a ruler alongside the box, with the zero mark where the wedge touches the box. The length the ruler should face away from the wedge (running parallel to the side of the box).
Push on the wedge so that it slides 2 inches (5 cm) under the box. Use another ruler to measure how high the end of the box is raised above the table.
On a piece of paper, draw two parallel vertical columns. Label the heading on one column Distance Wedge Moved and the other column Height Raised. Write the measurement under the first heading and the distance the box was raised in the secind column.
The Constant in this project is the incline (the slope) of the wedge, the box it is lifting, and the force applied. The Variable is the distance the wedge is moved inward and the height it pushes up on the box.
Now push the box forward another inch or centimeter, and record the height raised. Continue to push the wedge under the box at each increment, until the top of the wedge is reached. Write down the distance and the height for each move increment.
Results and Conclusion: Write down the results of your experiment. Come to a conclusion as to whether or not your hypothesis was correct.
Something more: A wedge doorstep is a stationary wedge that is applying a force equal to the force needed to keep the door from closing.
A nail is also a wedge. Can you imagine pushing something into a piece of wood that doesn’t come to a point. The smaller the nail, the easier it is to wedge into the wood, because it has less wood material to push out of the way. Try pushing a nail into a piece of wood by hand. Then try pushing a thumbtack with a head on it into the same piece of wood. Is the thumbtack much easier to push in?