Forces and Newton's Laws

Student Learning Objectives
Lessons / Lecture Notes
Important Equations
Example Problems
Applets and Animations

Student Learning Objectives

• To understand and use Newton's 1st, 2nd, and 3rd laws.
• To recognize what does and does not constitute a force.
• To identify the specific forces acting on an object.
• To draw and make effective use of free body diagrams.
• To understand the connection between force and motion.
• To learn a strategy for solving force and motion problems.
• To identify action/reaction pairs of forces.
• To distinguish between mass, weight, and apparent weight.

Lessons / Lecture Notes

The Physics Classroom
(conceptual)

PY105 Notes from Boston University (algebra-based):

Introductory physics notes from University of Winnipeg (algebra-based):

HyperPhysics (calculus-based)

PHY2048 notes from Florida Atlantic University (calculus-based):

PHY2043 notes from Florida Atlantic University (calculus-based)

General Physics I notes from ETSU (calculus-based)

Important Equations

Example Problems

Problem 1
In the figure below, two forces, F1 and F2, pull a 50.0 kg crate. The magnitude of F1 is 215 N and it is applied at a 42.0o angle. The magnitude of F2 is 55.0 N. If the crate is accelerating to the right at a rate of 0.500 m/s2, find the coefficient of kinetic friction between the crate and the floor. (Solutions)

Problem 2
In the figure below, a block of weight w1 = 100.0 N on a frictionless inclined plane of angle 15o is connected by a cord over a massless, frictionless pulley to a second block of weight w2 = 30.0 N. (a) What are the magnitude and direction of the acceleration of each block?  (b) What is the tension in the cord? (Solutions)

Applets and Animations

 Forces in 1 Dimension Explore the forces at work when you try to push a filing cabinet. Create an applied force and see the resulting friction force and total force acting on the cabinet. Charts show the forces, position, velocity, and acceleration vs. time. View a Free Body Diagram of all the forces (including gravitational and normal forces). Friction Learn how friction causes a material to heat up and melt. Rub two objects together and they heat up. When one reaches the melting temperature, particles break free as the material melts away. Hooke's Law A simple animation illustrating Hooke's Law Inclined Plane The applet show a mass sliding down an inclined plane. The can control the initial velocity of the mass as well as the coefficient of friction. The Ramp Explore forces, energy and work as you push household objects up and down a ramp. Lower and raise the ramp to see how the angle of inclination affects the parallel forces acting on the file cabinet. Graphs show forces, energy and work. Roller Coaster The Roller Coaster model explores the relationship between kinetic, potential, and total energy as a cart travels along a roller coaster.  Users can create their own roller coaster curve and observe the resulting motion. Forces on a Pendulum The weight, force due to tension, and total force exerted on the bob of a pendulum are shown. (Interrupted) Pendulum This applet displays a pendulum oscillating back and forth. The user can vary the height of a pin so that the pendulum’s path is interrupted. Conical Pendulum This applet shows a conical pendulum (i.e. a mass connected to a string rotating in a horizontal circle). The user can control the length of the string and the frequency. Mass Moving in a Vertical Circle A mass is in circular motion in the vertical plane. We show the weight and force exerted by the tension in the string.