Weights on Strings
PIRA: 1F20.10
Overview:
Inertia measures the difficulty of changing an object’s velocity. When we have our weights and strings set up, the mass of the weight makes it much more difficult to move. When we pull the bottom string really fast, there isn’t enough time for the weight to react, so the string breaks below the weight. When we pull the string slowly, the string will break above the weight due to the force of you pulling plus the force from the weight.
Materials:
2x 1kg weights
3x metals rods
2x 90॰ clamps
2x table clamps
Foam pad
Thin string, yellow string is found in the outreach room in bin F4
Setup:
Put a table clamp on each side of a corner on a table. Put a metal rod in each of the table clamps, then put a 90॰ clamp near the top of each metal rod. Take the third metal rod and clamp it in both of the 90॰ clamps, making a frame. Adjust the frame so that it is facing the students as much as possible, but will still allow the weights to fall onto the table without bouncing onto the floor. Tie the yellow string to the top of each weight and to the metal rod going across the table. The weights should hang almost halfway between the rod and the table. Tie another string to the bottom of each weight long enough to touch the table (extra is okay). Place the foam pad underneath the weights.
How to:
Ask the students their predictions as you plan to pull one string down quickly, and the other slowly. Wrap your finger around the lower string of one of the weights. Slowly pull on it until the string above the weight breaks, and watch your fingers as it falls. Take the string on the bottom of the second weight and wrap it around your finger. Pull the string as fast as you can without injury.
Safety:
Watch out for falling weights, they may bounce and fall onto someone’s foot.