PHY221 Ch5: Forces and FB Diagram

1. Recall main points: Forces and FB diagrams2. Discussion and examples

PHY221 Ch5: Forces and FB Diagram1.

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Forces: Gravitational Force

Expression:

Miracle of mass (inertia) and gravitational mass:

Weight: Grav force at SURFACE of EARTH

PHY221 Ch5: Forces and FB Diagram1.

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Forces: Empirical forces

Contact Forces: Normal and Tension

Other Forces: Spring restoring force

PHY221 Ch5: Forces and FB Diagram1.

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Free Body Diagrams and example of problems

Box Pushed Up an Incline at constant velocity (q=30o m=200kg; What is the push needed?)

PHY221 Ch5: Forces and FB Diagram2.

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Person in elevator at a. What is the reading on the scale?

PHY221 Ch5: Forces and FB Diagram2.

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Car goes in curve of R=25m at v=5m/s. Find tension in string holding fuzzy die?

PHY221 Ch5: Forces and FB Diagram2.

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Summary: Force problems

• Picture: Free Body Diagram: • Identify all forces acting on m: Tension, normal, weight, others…• Draw the forces on m from origin in object: direction is usually known

but mag unknown (tension, normal, etc…)• Choose axes x and y: always take un axis // acceleration if a is not zero.

Otherwise (v=cst) choose axes to facilitate projection of forces on axes.• Write all vector in terms of mag, angle expressions.• Write F=ma along each axes in terms of previous result• Solve

Ch 5: Assignments

Ch 5: Assignments

Ch 5: Assignments

Ch 5: Assignments

Ch 5: Assignments

Ch 5: Assignments