Eighth-grade physics classes introduce the most basic tenants of physics. The curriculum revolves around the scientific method and lab work. Although eighth-grade physics labs do not get into the deeper ideas that high school and college ones do, the projects can be interesting and just as fun.
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Whenever doing any science experiment, have an adult supervise the students at all times. For pulley projects, an adult should set up the pulley systems and double check their functionality and safety. You need a sturdy surface from which to suspend the pulleys; the strength of the surface depends on the mass of the object you intend to lift; lab stands work well for smaller objects. Check that everyone has and wears safety glasses and closed-toed footwear.
A basic pulley looks like a thick disk with a groove in the middle. You use this groove to run the line through the disk. The pulleys in a block and tackle system resemble a basic pulley, but block and tackle systems have at least two pulleys. Each pulley has multiple grooves that allow you to thread the rope through one groove, down around another pulley and back up and around the first pulley.
Introduction to Pulley Systems
Determine the mass of an object and have each student lift it by hand. Set up three different systems: one pulley, two pulleys and a block and tackle system. For consistency, the students should lift the same object each time and to the same height. Ask students to rate each of the four systems from one to 10 with one being the easiest to lift and 10 being the most difficult. This project works well as an introduction to pulley systems. Use it to give students an example of the advantage pulleys give humans for lifting large objects. You can also use the lab to introduce units common to physics such as grams and newtons.
The homemade elevator gives students an idea of how elevators function and how physics shows up in the world every day. Cut out four 6-inch by 6-inch squares of cardboard. Stand the squares on end and tape them together at the edges making a four-sided box with no top or bottom. Cut a 2-foot by 2-foot piece of plywood, and lay the board flat on a hard surface.
Part 2: Elevator Pulley System
Stand up an empty thread spindle in the upper left corner of the plywood board, one inch in from each side. Run a nail through the spindle's centre hole and into the plywood. Make sure the spindle can easily rotate on the nail without falling off. Measure over 4 inches from the centre of the spindle and make a mark. Line up the centre of a second spindle with the mark. Nail down the second spindle in an identical manner. Nail down two more spindles, 4 inches apart, in the same manner as you did the first and second one. Start at the bottom left corner, one-inch in from each side, and attach two more spindles in the same way. Try to keep your spindles in line with one another; this will allow the pulley system to rotate more smoothly. You now have four spindles across the top and two on bottom left side.
Part 3: Elevator Car
Set the cardboard box in the centre of the plywood so the open ends lie parallel to the board. The board should cover one of the open ends with the other facing the sky. Poke two holes in the bottom of the cardboard box centring them the best you can. Make a one-inch distance of cardboard between the holes. Poke two holes in the top of the cardboard box the same way you poked the bottom holes. Starting with the bottom, run a string up through the right side hole, into the box, over the one-inch cardboard gap and back down and out the other hole so it sticks out the bottom of the box. Tie the string back to itself so it makes a connected loop through your holes and hangs off the bottom, outside of the box.
Part 4: Elevator Cables
Run the string down and under the two bottom spindles, up the left side of the board and over the two left side top spindles. Run the remaining end of the string through the right-hand hole in the top of the box so the end hangs inside the box. Pull the string taut around the spindles and knot the end so it cannot slip out of the hole. Knot one end of another piece of thread so it cannot pass through the box's top, left-hand hole. Run the unknotted end of this string through the hole and over the two spindles on the top right side of the board. Tie a key or bolt around the remaining end of the thread to act as a counter weight. Try rotating different spindles and observing their effect on the elevator. Ask the students to predict the effect that a specific spindle rotation will have.
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