5 Newtons Third Law of Motion Force as

5 Newton’s Third Law of Motion • • Force as an interaction Newton’s 3 rd 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 3 rd 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 3 rd 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