Your Bedroom Door and Torque

Appropriate Age Level
5+ (math for older children 10+ , concepts for younger children 5-9)

Science Concepts Learned

Torque (τ) : the ability for an object to rotate around (spin around) an axis when a force (a push) is applied.

τ= rFsinφ
r=radius (m) (probably will be measuring in cm and will have to convert)
F=Force (N)
φ = angle of rotation 

Materials Needed

Hinged Door
Protractor

Activity/Experiment

1. Explain that a door has torque, and that the hinges are its axes. 

2. Have the child pick 3 different distances, about the same distance apart at the middle of the door.

3. Have the child push the door with the same strength at each distance/radius. (If you are doing the math portion of this experiment, measure each radius from the end of the door and assign 1N for the arbitrary amount of force being used.)

4. Discuss how it was easier to push the door further away from the hinges than closer because it has more torque due to the radius being longer, and that it was harder closer to the hinges because it has less torque.  (If doing the math part here, plug in the numbers, and also use a protractor to see the angle associated with the movement, place the protractor at the end of the door where the hinges are to get the most accurate measurement. The protractor should have one side where the door started and the other where the door ended when pushed.) 

5. Now have the child push the door with 3 different strengths at the same point in the door.  (Measure angles again with the protractor, and use 1, 2, and 3 N as the force increases smallest push to biggest push)

6. Discuss how the differences in pushes made the door swing different amounts, the smallest push was the smallest force and therefore had the least amount of torque etc.

7. And there you have it torque!

Time Allotted 

15-30 depending on how quickly the math is carried out

Physics for Scientists and Engineers 5th Ed. 2000