LEVERS AT WORK

Find out how to make three different kinds of lever in these experiments. The first is a can crusher that uses a lever action to squash a can. The second is a gripper for picking up small objects, just like a pair of tweezers. It can also work as a nutcracker. In a pair of nutcrackers, the load (in this case a candy or a nut) is between the pivot (the pencil) and the effort (where you push). In a pair of tweezers, the effort is between the pivot and the load.

The third experiment is a balance scale. It is like the ones used by the Romans about 2000 years ago. It works by balancing the weight of an object against a known weight, in this case a bag of coins. The coins are moved along the lever arm, until they balance the object being weighed. The farther away from the pivot the weighed bag is, the greater turning effect it has on the lever arm. The heavier the weight being measured, the farther away the bag must be moved to balance the arm. The weight is read against the scale along the arm.

CAN CRUSHER

Two short planks of wood about 16 x 4in and ½ - ¾in thick, hinge, screwdriver, two coffee-jar lids, glue, empty can.

STEP 1
Lay the two planks of wood end to end. Ask an adult to help you screw them together with a hinge, using screws and a screwdriver. Make sure the hinge is secure.

STEP 2
Glue a jar lid to the inside edge of each plank wood, with the top of the lid face down. The lids should be about halfway along each plank and the same distance from the hinge.

To crush a can, put the can in between the lids, so that it is held in place. Press down hard on the top piece of wood.

GRIPPER

Short pencil, two pieces of wood each about 6in long, thick rubber bands, objects to pick up or squash, such as candies or nuts.

STEP 1
Put the pencil between the two pieces of wood, near one end. Wrap the rubber bands tightly around the places of wood to make a pivot. You have now made the gripper.

STEP 2
Hold the gripper near the pivot to make it act like a pair of tweezers. See if you can pick up a delicate object, such as a candy or a grape, without crushing the object.

STEP 3
Hold the gripper at the end farther away from the pivot. Now your lever operates as a pair of nutcrackers. The effort at the point you push is increased.

BALANCE SCALE

Thick card about 20 x 3in, thin card, scissors, string, ruler, hole punch, 4 ½in circle of card, tape, 4oz of coins, felt-tipped pen, objects to weigh.

STEP 1
Make the arm by folding the thick card in two. Make a loop of thin card and fold it loosely around the arm 4¼in from one end. Tie a piece of string to this support.

STEP 2
Make a hole ½in from the arm’s end. Make the card circle into a cone. Tie it to the hole. Make an envelope from thin card, and tie it to a loop so that it hangs over the arm.

STEP 3
Put the coins in the envelope and seal it up. Starting from the middle of the support, make a mark every 2in along the arm. This scale will tell you the weight of an object.

To weigh an object, put it in the cone and slide the envelope of coins backward and forward along the arm, until the arm balances. Each mark along the scale equals 2oz. In this picture, the object being weighed is about 3oz.