# Natural Science - Year I

#### Unit 14 Lab: Simple Machines

Lab Assignment for Unit 14

 This Unit's Homework Page History Lecture Science Lecture Lab Parents' Notes

# Natural Science Unit 14 Laboratory Activity: Simple Machines

## Goal: To determine the mechanical advantage of an inclined plane

### Materials and Equipment:

• an flat surface on which you can slide things without worrying about scratching it. You should be able to change the elevation or incline of the surface [scrap wood on a table will work--but it shouldn't be too rough].
• several sliders: such as a block of wood, a bar of soap. They should have flat surfaces where they will be in contact with the support surface.
• sandpaper
• pins, tape, or other means of fastening string to your slider.
• string
• a set of standard weights (I like using coins; try to weed out any that are too worn). These do not have to be any particular unit, but they should all be the same.
• a bucket, sack, or other means of keeping the weights together.
• blocks or other means of inclining your slide surface
• protractor

### Procedures:

1. Weigh your slide; you might use a kitchen scale.
2. Set up the slide on the surface without the sandpaper.
3. Fasten the string to your slide
4. Run the string over the edge of the surface so that it hangs down; fasten your cup or other weight holder to the end.
5. Start adding weights to the end of the string.
6. Record the total amount of weight required for your slide to start moving.
7. Repeat the above procedure, but this time, have the slide start on a piece of sandpaper (the sandpaper should be fastened to the surface so that it cannot move.
8. Repeat the above procedure with another slide which has a noticeably smoother or rougher surface.
9. Repeat the above procedure for each slide with the slide surface inclined at approximately 10° and at 15°.
10. Make a table which shows the weight of the slide, the type of surface on which you started it, the inclination of the surface, and the weight required to overcome static friction.
11. The weight at which the slide starts to move is a measure of the force necessary to overcome the static friction holding it back. Mechanical advantage is the ratio of load (the weight of the slide) divided by effort, or the force necessary when a machine is used (in this case, an inclined plane). Determine the mechanical advantage of each situation above. When is the mechanical advantage the greatest?