General Equipment
Here is the set of equipment we need for this lab :
- 1 Force probe
- 1 Motion sensor
- 2 USBLinks (1 shown)
- 1 Box weights
- 1 strings
- 1 wooden block (w/ felt)
- 1 small plastic ruler (for measuring length of rubber band stretch)
- 1 sandpaper sheet
Readying Force probe
We want to mount the force probe in this orientation for the first part of the lab.
Click the ZERO button before making measurements.
Adding mass to the block
Make sure the block has the wood side down, and then the masses can go on the top felt side (if the felt side is down, it will slide too easily - we are trying to investigate FRICTION!). The masses themselves should provide enough of an "object" to see for the motion detector.
Motion detector "sees" object
Here is the setup on the lab bench - the paper is taped down (we will most likely use sandpaper in this step - gives better friction - go figure!).. that is the "surface" the block will slide along. Make sure the motion detector is at least 50 cm away from the near edge of the paper. In this image, the force probe would be pulled to the left ... so the force probe measures the frictional force, and the motion detector can determine exactly when the block "broke free" from the surface, and started moving.
Getting a good friction graph : It is challenging to pull very slowly with the force probe while the block is still not moving, until the block breaks free ... keep trying until you get a good "rising graph until there is a peak, then a drop to the constant kinetic friction" type graph - patience will be rewarded with a good graph!
A sample "good" graph is shown to the right - notice the peak, the drop-off and then the constant force while the velocity is reasonably constant.
