The Greek Archimedes once said that given a fulcrum and a lever, he could move the world. Levers are another simple machine. What is it and how does it work?
Question: How do levers work?
Materials:
Wood slat 40 cm long by 5 cm wide
Triangular or 1” wood block [I found the 1” block works best.]
Several weights, 2 the same, 1 heavier, 1 lighter
Scale
Ruler
Pencil
Procedure:
Place the block on a table
Note: This is your fulcrum.
The slat is not exactly level. This shows as my measurement of each end gave two slightly different values.
Place the wood slat on the block moving it back and forth until it balances
Note: The slat is your lever
Mark the balancing point
Measure from the end of the slat to the line from both ends
Mass your weights unless they are from a weight set so you know the masses
Keeping the balancing point over the fulcrum, place a mass at one end of the slat
Placing a mass on one end causes that end to drop to the table while the other end rises.
Observe what the lever does
Place the identical weights, one at each end
Adjust the slat until it is again in balance
Take one weight off
Place the light weight on the other end of the slat
A teeter totter on a playground behaves this way when a heavier person sits down on one end. How can this person make it balance so both people have fun?
Move the slat back and forth until it balances
Measure the distance from the balance point over the fulcrum to each weight
Remove the weights
Return the slat to the original balancing line
Place the heaviest weight on one end of the slat and a lighter weight on the other end
Predict how you will need to move the slat to balance the two masses
Move the slat until the two are in balance
Observations:
Mass of weights
Distances:
From ends to balancing line
From masses to balancing line
Same mass weights
Mass and light mass
Mass and heavy mass
Describe what happens:
When you balance the slat
When one mass is put on one end of the slat
When the two identical weights are on the slat
When the light weight is put on one end
When the light weight is balanced
When the heavy weight is put on the slat
Prediction of where the slat will balance
When the heavy weight is balanced
Analysis:
Multiply the mass times the distance for the two identical masses
Multiply the mass and distance for the mass and the light mass
If you consider the formula of Fd = Fd it explains why a heavy mass is at a short distance to balance with a light mass.
Multiply the mass and distance for the mass and the heavy mass
Conclusions:
Compare the lengths when the salt is balanced.
If you could mass each end of the slat, how do you think these would compare?
Draw the lever, fulcrum and one mass
Put arrows to show where the forces are acting on the lever system
The mass exerts mass downward on one end of the lever. That puts an equal upward force under the other end. The force vectors are equal and opposite so the center, on the fulcrum, has no net force acting on it.
Why does the slat balance at the same place when two equal masses are balanced?
How does the mass x distance results compare for the two identical masses?
How do these results compare for the light weight and the heavy weight?
A rule for levers is that the force times the distance for one arm or side equals the force times the distance for the other arm or side. Do you think this is correct? Why do you think this?
How can this be used to move a heavy object?
What I Found Out:
I tried using a triangular fulcrum. The slat would balance on the edge but it was very difficult to do this. It worked much better to use the 1” board piece as a fulcrum. I did have to watch that the slat was level as it would balance a little before it was really level.
I was in a hurry. I hope you take your time. My lever is not quite balanced between the 20 g and 50 g masses. You can tell because the slat is not level.
When I balanced the slat on its own, the ends measured 37.0 cm and 38.7 cm. This was nearly equal. The two ends would have the same mass as the slat would be divided in half.
The mass pushes down on the lever so it sinks to the table top. That means a force is pushing up the other end.
When I put masses of equal mass on the ends of the slat, the force pushing on each end was the same, the total mass of each end remained the same so it would balance at the same place as it did without the masses.
The balancing point puts equal mass on each side of the fulcrum. since the masses are equal, the rest of the set up is equal.
My two equal masses gave 740 g-cm and 772 g-cm. When I looked at the pictures of this, the slat wasn’t completely level so the two were probably even closer in size.
When I balanced the lighter mass, the slat moved the heavier mass closer to the fulcrum. The distances were 30.0 cm for the 50 g mass and 43.0 cm for the lighter20 g one. This gave the Fd values as 150 g-cm and 91.2 g-cm. The distances for the 500 g mass was 13.0 cm and 62.6 cm for the 50 g mass. The Fd values were 6500 g-cm and 3030 g-cm.
The Fd values for my experiment weren’t very close. This is the rule a lever normally follows so I need to look over my Procedure and Observations more closely.
The idea of a simple machine is to do the same amount of work using less effort. A lever would do this if the distance to the heavy object was short and the distance to where the force is applied is long. A long distance times a small effort will equal and larger effort over a short distance.