Activity 4

1. Student A will be the force (F) and students B and C together will be the load (L). Be sure that students B and C together are heavier than student A.

2. Weigh yourself using a bathroom scale.

3. Go to a playground where you can find a seesaw. Take a measuring tape with you.

4. Using the measuring tape, measure the distance between both seats and the centre of the seesaw. These distances will be the force arm (d1) and the load arm (d2).

5. Each student sits on their seat. Students B and C try to sit as close as possible to each other. What happens to the seesaw?

6. In the picture below, the force F tries to turn the seesaw anticlockwise and the load L tries to turn it clockwise. Remember that this tendency of a force to rotate an object around an axis is called the moment of force.

Multiply force F by its arm d1 and you will get the moment of force (MF).

Multiply load L by its arm d2 and you will get the moment of load (ML).

Choose the correct sentence and write it under the table:

CORRECT SENTENCE:

7. To get the seesaw balanced, both moments should be equal:

Mf=ML

so:

F · d1 = L · d2 This equation is called

the law of the lever

But the ratio of load to force is the mechanical advantage of a simple machine. So:

8. Isolate d2 in the law of the lever and you will find out the distance you have to locate the load to balance the seesaw.

9. Check the result changing the position of students B and C to the new distance d2.

10. Work out the mechanical advantage of the seesaw with the new distance d2.

MA=

11. Fill in the gaps with the appropriate words and you will get some conclusions:

Thanks to the .......... we can move a big .......... (students B and C) making a small .......... (student A) because the force .......... (d1) is much longer than the load .......... (d2).

The shorter the load .......... (d2), the smaller the .......... (F) needed to lift the ..........(L). The longer the force .......... (d1), the bigger the .......... (L) we can lift.

The .......... .......... (MA) of a .......... is the ratio of the .......... arm (d1) to the load .......... (d2).