m03-1: force and motion-i (part 1)

5-1 Newton’s First and Second Laws (1 of 20) Link to heading

Learning Objectives

5.01 Identify that a force is a vector quantity and thus has both magnitude and direction and also components.
5.02 Given two or more forces acting on the same particle, add the forces as vectors to get the net force.
5.03 Identify Newton’s first and second laws of motion.
5.04 Identify inertial reference frames.

5-1 Newton’s First and Second Laws (2 of 20) Link to heading

5.05 Sketch a free-body diagram for an object, showing the object as a particle and drawing the forces acting on it as vectors anchored to the particle.
5.06 Apply the relationship between net force on an object, its mass, and the produced acceleration.
5.07 Identify that only external forces on an object can cause the object to accelerate.

5-2 Some Particular Forces (1 of 15) Link to heading

Learning Objectives

5.08 Determine the magnitude and direction of gravitational force on a mass, for a given free-fall acceleration.
5.09 Identify that weight is the magnitude of the net force required to prevent a body from falling freely, measured by the frame of ground.
5.10 Identify that a scale gives an object’s weight when the measurement is done in an inertial frame but not in an accelerating frame, where it gives an apparent weight.

5-2 Some Particular Forces (2 of 15) Link to heading

5.11 Determine the magnitude and direction of the normal force on an object when the object is pressed or pulled onto a surface.
5.12 Identify that the force parallel to the surface is a frictional force that appears when the object slides or attempts to slide.
5.13 Identify that a tension force is said to pull at both ends of a cord (or a cord-like object) when the cord is taut.

5 Summary (1 of 4) Link to heading

Newtonian Mechanics
- Forces are pushes or pulls
- Forces cause acceleration
Force
- Vector quantities
- 1 N = 1 kg m/s2
- Net force is the sum of all forces on a body

5 Summary (2 of 4) Link to heading

Newton’s First Law
- If there is no net force on a body, the body remains at rest if it is initially at rest, or moves in a straight line at constant speed if it is in motion.
Inertial Reference Frames
- Frames in which Newtonian mechanics holds

5 Summary (3 of 4) Link to heading

Mass
- The characteristic that relates the body’s acceleration to the net force
- Scalar quantity
Newton’s Second Law $$\tag{5-1} \vec{F}_{\rm net} = m \vec{a} $$
- Free-body diagram represents the forces on one object

5 Summary (4 of 4) Link to heading

Some Particular Forces
- Weight: $$\tag{5-12} W = mg $$
- Normal force from a surface
- Friction along a surface
- Tension in a cord

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