Picture yourself helping to push a car. You shove. You turn around and push with your back. The car doesn’t move. Did you do any work?
According to your muscles you did a lot. According to the physics definition you did none.
In physics work is defined as moving something over a distance. Since the car did not move, you did no work. In physics this is written as: W = FD or work equals force times distance.
Question: How much work do you do?
Spring scales [My set of 3 has a sensitive scale, a medium scale and a harder scale.]
Several blocks of different masses
Note: Another solution is to have stackable blocks.
Each block will need a small loop to hook the spring scale to. An easy way to make such a loop for lighter blocks is to take a length of masking tape, attach one end to the block, crimp a length of the tape and attach the other end beside or over the other end on the block.
Place a block on a smooth table top
Set the ruler so you can see how far you will move the block
Hook a spring scale to the block
Pull the block steadily for 30 cm
Observe the amount of force on the scale in grams
Note: If the scale barely moves, try a scale with a more sensitive scale on it.
Repeat this for each block or additional block
Record the distance and force for each block
Multiply the grams times the distance in centimeters for each block to get the work done for each block.
Which block has the most mass? Why do you think so? [You can check this by massing the blocks.]
Do you do more work moving a block with less mass or more mass?
If you pulled a block 15 cm, would you do more or less work? Why do you think this?
What I Found Out:
I used some scrap wood pieces for blocks so they came in various sizes and shapes. The biggest one was the one I chose to put the loop on. the others were piled on top of it one by one to increase the mass pulled by the spring scale.
The first block took 6 g to pull it the 30 cm. This made the work done 180 g-cm.
Two blocks took 40 g to pull the same distance. Now the work done was 1200 g-cm.
Three blocks took 49 g to pull. Now the work done was 1470 g-cm.
Four blocks took 52 g of effort making the work done 1560 g-cm.
Five blocks took 75 g of force making the work done 2250 g-cm.
Six blocks took 85 g of force making the work done 2550 g-cm.
Seven blocks took 90 g of force making the work done 2700 g-cm.
The more blocks on the pile, the more force it took to pull the pile across the table. That makes me think a heavier block will take more force than a lighter one.
Looking at the increases in effort, the first block took 6 g but the second took an additional 34 g so the second block must have more mass than the first one.
The third block increased the force 9 g and the fourth a mere 3 g. These are lighter than the second block.
The fifth block increased the force needed 23 g. The sixth added 10 g and the last one 5 g. The second block was the biggest block with the fifth block next.
Pulling the first block 30 cm required work of 180 g-cm. If I had pulled the block only 15 cm, it would be 6 g times 15 cm or 90 g-cm. It takes less work to move half the distance.