Types of Force

1. Types of Force In this lecture you will learn about pressure(PSI), different types of force, and be introduced into a stress strain diagram.

2. The beginning… • A force is some measurement of the amount of energy it takes to do something. • Other ways to measure force are Newtons, kilograms, grams, stones… • An area is a measurement of a 2D space. • Other ways to measure area are square Meters, square inches, square feet, square yards, square mile…

3. What is PSI? • Pounds per square inch • It measures pressure • Pressure is force and area other measures of pressure. PSF, Newton per meter square…. Any combination where a force is over an area. Which would you rather get stepped on by?

4. How do you calculate PSI (or other pressure measurements) • Force divided by area • Or lbs/inch^2 • If you had a force of 10 pounds and an area of 5 inches square your PSI would be_______?

5. Here is an example • If the weight was the same which would hurt more? • Converse = 48” square • High heel = 18” square • Just the heel = .75” square • Assuming the force is the same • (200 lbs) • 200lbs/48” square = 4.16 psi • 200lbs/18” square = 11.1 psi • 200lbs/.75 square = 266.6 psi

6. Discussion • Can you think of one example where varying the shape of something changes the pressure and how it is used. • You have 2 minutes to come up with an interesting example and share with your table. • I will call on each group to speak at the conclusion of that time.

7. Other types of measures.. • PSF is used in the building industry • A classroom is required to withstand 40 PSF • A hallway is required to withstand 100 PSF • An attic is required to withstand 10 PSF • Pascal is used in the metric system and is a Newton per meter square

8. One way pressure is used by engineers? • Engineers and materials scientists need to know how much pressure a given type of material can take. • To do this they break a material sample. • The same sample can withstand different amounts of force depending on the type of force. Stress strain machine

9. Types of stress

10. Discuss… • Group up at your tables and come up with a tool or process that uses one of the types of force I introducedand how it uses that force. • Be ready to share out the answer… anyone could be it….

11. Deformation • When materials have a force applied they change shape • Sometimes it is a permanent shape change • If they permanently change shape without cracking it is called plastic deformation • If the material springs back it is called elastic deformation

13. Discuss… • Which type of steel would be best for making a sword and why?

14. Young’s modulus • Engineers are very concerned about the straight potion of the stress strain curve. • The equation below show how to calculate this. • E is the Young's modulus (modulus of elasticity) • F is the force exerted on an object under tension; • A0 is the original cross-sectional area through which the force is applied; • ΔL is the amount by which the length of the object changes; • L0 is the original length of the object.

15. Young’s modulus To determine young’s modulus from a deflection test you need these equations • Square materialsE = W L^3 / 4 Δ b h^3 • W=weight (or force) • L= length of beam from support • B= base • H =height • Δ = Amount of deflection • Round materials E = 4 W L^3 / 3 π Δ d^4 • D= diameter of round material