Pressure- Bed of Nails (Lupe Anaya)

Author

Lupe Anaya

Principle(s) Illustrated

Pressure is the application of force over an area: P=F/A
Pressure and area are inversely proportional: the greater the area a force is applied over, the pressure experienced is smaller
Distribution of weight

Standards

Physical Science: Forces
- 8 2a: Students know a force has both direction and magnitude
Physical Science: Forces
- 8 2d: Students know how to identify separately the two or more forces that are acting on a single static object, including gravity, elastic forces due to tension or compression in matter, and friction.
Investigation and Experimentation
- 1d: Formulate explanations by using logic and evidence

Questioning Script

Prior knowledge & experience:

Students know that a sharp object can pop a balloon.

Students have experienced being poked by the tip of a pencil.

Some might have experienced being stepped on by a high heel...ouch!

Root question:

What happens if I poke the balloon with one nail? Two nails?

What do you think will happen if I push down on the balloon lying on a bed of nails?

Why can you easily pop a balloon with one nail but not so easily on a bed of nails?

What would happen if there were less nails on the board, or if they were spread farther apart?

Target response:

The balloon pops with one nail because the force applied is concentrated in a small area, therefore, the pressure is high enough to pop the balloon. When the balloon is on the bed of nails, its weight and the force applied is distributed over a larger area, thus decreasing the pressure on each nail. More force is now needed to pop the balloon.

Common Misconceptions:

If one nail pops a balloon with little force, then the bed of nails should pop it rather quickly and with less force.

Connections/Extensions:

1. Why is it painful to be stepped on with high heels? Why is it painful to wear them? Explanation.

2. What exerts more pressure, a woman on high heels or an elephant? Why?

3. Razor blades that have multiple blades spread out the force exerted by any one blade over a larger surface area.

4. Why can you stand on several paper cups but not on one? View Lesson