5 Newton’s Third Law of Motion Force as an interaction Newton’s 3rd Law Systems Vectors and Vector Components

Forces and Interactions inter = between all forces are interactions between masses each mass feels same size force

What forces act on the man? Draw a Force Diagram for him.

Newton’s 3rd Law of Motion Whenever one object exerts a force on a second object, the second object exerts an equal and oppositely directed force on the first.

Force-Pairs in Action

Systems forces external to the system determine the systems acceleration systems are defined so unknown forces can be determined, e.g., tension can be determined below

What external forces act on this system?

Action and Reaction

Summary of Newton’s Laws First: Law of Inertia Second: Fnet = ma Third: Forces occur in pairs (equal size, opposite direction)

Force Diagram each object. Which has greater acceleration when released?

Page 21, 22 in Practicing Physics!!!

Vectors magnitude and direction represented by arrows examples: force, velocity, and displacement added to determine net force addition is done tail-to-head applies to velocity

Net Force as Vector Addition

Diagonal of Square is 1.41 times its sides

Which Plane has Highest Ground Speed?

Components of Vectors component = part horizontal part is the “x component” vertical part is the “y component”

Which strings have greater tension?

Practical Vector Addition

Another Use of Components

Summary All forces are interactions, i.e., part of a pair of forces Newton’s 3rd Law: pairs have equal size opposite direction Systems are defined to determine unknown forces Vectors, Vector Components, Parallelogram Rule

Practicing physics Do Page 27 Refer to page 26 to review parallelogram rule of vector addition