Download presentation
Presentation is loading. Please wait.
1
Newton's First Law of Motion
An object will remain at rest or move in a straight line at a constant speed if there are no forces acting on it. = Uniform motion with constant velocity is The natural state of an object.
2
Newton’s second Law Fnet = ma [kg m/s2 = 1N] To understand net forces, we need to know free-body diagrams.
3
Normal Force
4
Q1 The weight of the box is 70kg and the pulling force is 500N, the normal force will be about 200N pointing up; 200N pointing down; 1200N pointing down; 0N.
5
Q2 Adam stands in an elevator that is accelerating upward. The normal force acting him is A) larger than 500N; B) smaller than 500N; C) equal to 500N; D) Not enough information.
6
Newton’s third law Forces always come in action/reaction pairs
following the 3rd law: 1) Two members act on different objects; 2) They point in opposite directions; and are equal in magnitude.
7
Weight of a person in an elevator
8
Friction forces
9
Coefficients of friction
Static: S= max(fs)/n fs S n Kinetic: K= fk /n fk = K n, S > K
10
Q3 See page 114, “Stop to think 4.3”
11
Q4 You are pressing a book (m=1kg) against a wall. The static friction coefficient is 0.4. Which of the following is true for the friction on the book? The friction force is pointing downward; B) The friction force is pointing upward; C) The friction force is pointing away from the wall; D) The friction force is pointing into the wall.
12
Q5 You see that a box is at rest on the top of a car while the car is speeding up. What is the direction of friction force acting on the box? A) forward; B) backward; C) zero; D) depending on the velocity of the car.
13
Interacting objects (textbook, page 121 more on the 3rd law)
Similar presentations
© 2025 SlidePlayer.com. Inc.
All rights reserved.