Exam 1: Chapters 1-4 60% Problems – one problem from WebAssign with different numbers Understand homework problems Review notes and text Try new problems 40% Multiple Choice Questions Review Power Points (on web page) Review Before Class Assignments Try Questions Graphs, Pictures and Drawings (Sketches) Don’t rely on memorized equations

Chapter 5 The Laws of Motion 5-1a Force – a push or pull. CT1: The force of the elevator on Norbert and Zot is up. down.

Assume the elevator is near the Earth’s surface and that it is right-side up in the cartoon. CT2: The force of the non-sticky elevator surface on Norbert and Zot is up. down.

Assume the elevator is near the Earth’s surface and that it is right-side up in the cartoon. CT3: The acceleration of Norbert and Zot is up. down. zero

Figure 5. 1 Some examples of applied forces Figure 5.1  Some examples of applied forces. In each case a force is exerted on the object within the boxed area. Some agent in the environment external to the boxed area exerts a force on the object. NOTE: Old incorrect kick image underneath – a click reveals it. Fig. 5.1, p.113

5-1 B. Mass The mass of an object is the amount of matter (stuff) in that object. It is the same for a given object everywhere in the Universe. Mass is also called inertia because it resists being moved.

5-2 Newton’s First Law: A body remains in uniform motion (or at rest) unless acted upon by a net external force. acceleration due to Earth’s rotation  0.03 m/s2 acceleration due to Earth’s orbit  0.006 m/s2 acceleration due to Sun’s orbit  2 x 10-10 m/s2 An inertia frame of reference is a coordinate system (or frame) in which Newton’s Law’s hold. We will assume that the Earth’s surface is an inertial frame and not make errors greater than 0.03/10 = 0.3%.

CT4 A. B. C. D. E.

A. B. C. D. E. CT5

5-3 Newton’s Second Law: The net external force is equal to the mass times the acceleration. F = ma Force and acceleration are vectors Fx = max Fy = may remember Galileo! Fz = maz Normally we will do problems in a plane with only x and y components.

Calibrating a “Force Meter” Experiments show forces add as vectors.

Acceleration is Proportional to Force

Acceleration is Inversely Proportional to Mass

Applications of Newton’s Laws - Method Draw picture of the problem. Choose body (bodies) to isolate. Draw Free Body Diagrams (FBDs) for isolated bodies. Choose and label coordinate axes. Apply Newton’s 2nd Law: Fx = max and Fy = may Solve for F, m or a. Work out kinematics. Check solution is reasonable. P5.6 (p.136)

Concept Question 6 P5.6b: If the parachutist comes to rest over a shorter distance, the force exerted by the ground will be greater. less. the same.

FAB and FBA are 3rd Law pairs. 5-4 Newton’s Third Law: If body A acts on body B, then body B acts back on body A with a force equal in magnitude but opposite in direction. A B FAB FBA FAB and FBA are 3rd Law pairs.

A. C. B. D. E. CT7

Concept Question 8 P5.18b: If the 5 N force is applied to the heavy box instead, the contact force between the boxes will be greater. less. the same. P5.18 (p.137)

5-5 The Vector Nature of Forces Two Astronauts Pushing a Satellite with Forces that Differ in Magnitude and Direction

P5.22 (p.137)

P5.28 (p.138)

Orbit of Moon about the Sun Exaggerated and incorrect Actual

5-6 Gravitational Force or Weight Fg = mg (weight) g = -9.81 j (m/s2 ) x y Apparent Weight is the force you actually feel pushing on you – often the floor.

P5.35 (p.138)

Concept Question 9 P5.35b: If the constant speed of descent is greater than 1.1 m/s, the force of air resistance is greater. less. the same.

Concept Question 10 P5.33a: Your normal weight is 610 N and the scale in the elevator reads 720 N. The acceleration of the elevator upward. downward. zero.

Concept Question 11 P5.33c: Your normal weight is 610 N and the scale in the elevator reads 720 N. The magnitude of the velocity of the elevator is increasing. decreasing. zero. impossible to determine without more information.

5-7 Normal Forces The Normal Force May Equal the Weight

The Normal Force May Differ from the Weight

An Object on an Inclined Surface P5.42 (p.138)

Concept Question 12 P5.42b: If the angle of the incline is decreased, the normal force will increase. decrease. stay the same.

CT13 A. B.