# Newton's Third Law of Motion

```Today’s special
Hw check – vocab
Test results
Notes
HW for next time:
HW I due
Newton’s Third Law of
Motion
PAe.7: Explain the motion of objects on the basis of
Newton’s three laws of motion: inertia; the relationship
among force, mass, and acceleration; and action and reaction
forces.
PAa.1: Generate hypotheses on the basis of credible,
accurate, and relevant sources of scientific information.
PAa.2: Use appropriate laboratory apparatuses, technology,
and techniques safely and accurately when conducting a
scientific investigation.
PAa.9: Use appropriate safety procedures when conducting
investigations.
Question
When a rocket blasts off, if it was
not near the ground, would it take
off?
Newton’s Third Law
Whenever one object exerts a force
on a second object, the second object
exerts an equal and opposite force on
the first
Simple rule
Action: Object A exerts force on
object B
Reaction: Object B exerts a force on
object A
Action and reaction
Effects on objects differ if their
masses are different
a = F/m
Decreasing mass makes the
acceleration greater
Action and reaction forces act
on different objects
Forces cancel only when they act on
the same body
Donkey cart
Equal and opposite?
Donkey pulls and cart and pushes on
Bull fights
Why are they dangerous?
Tug-of-war
How does it work?
Question
When a rocket blasts off, if it was
not near the ground, would it take
off?
Homework
Chapter Review HW: pp. 80-82
I. Review questions2-20 even (due
date: ____________)
II. Exercises 2-20 even; Problems 18 (due date: __________)
Today’s special
HW check; Q &amp; A
Lab
Newton’s Laws video
Lab due next time! Don’t forget to
Today’s special
Turn in lab on front table
Some equations for HW II
Work on HW II with table partner
(work on problems, first!)
Handout: Newton’s 3rd Law
New seating chart
Some equations for HW II
F=ma
a=v/t
F1=-F2
Example
Billy rides his bike from rest to 8 m/s
in 4 s. How much force did Billy apply
to his bike if he and his bike have a
mass of 75 kg?
Example
Sally pushes her skateboard with a
force of 5 N. The skateboard has a
mass of 2 kg. How fast is it going
after 3 seconds?
Today’s special
HW II check
Computer project
Practice Test on Smartresponse
corrections before turning in next
class
Test 4 next time!
Today’s special
Turn in Practice test on front table
Test 4 Newton’s 3rd Law, enter MC