Lesson #14_Newton's Three Laws of Motion.pdf

3 Laws of motion

1. Prepared by: Muriel Grace G. Vierneza
2019
Newton’s Laws of
Motion
GENERAL PHYSICS 1`

2. ➢How will you relate inertia in getting the
ketchup out of its bottle?

3. Inertiaisthepropertyofmatterinwhichanobject
thatisatrestwantstoremainatrest,andan
objectthatismovingwantstoremainmovingina
straightlineunlessanotherforceactsuponit.
Abodyactedonbyno
netforcemoveswith
constant velocity
(whichmaybezero)
andzeroacceleration.
ΣF = F1 + F2 = 0

4. 1
st
Law
•Once airborne,
unless acted
on by an
unbalanced
force (gravity
and air –fluid
friction), it
would never
stop!

5. Newton’s 1
st
Law and You
Don’t let this be you. Wear seat belts.
Because of inertia, objects (including you) resist
changes in their motion. When the car going 80
km/hour is stopped by the brick wall, your body
keeps moving at 80 m/hour.

6. Why then, do we observe
every day objects in motion
slowing down and becoming
motionless seemingly without
an outside force?
It’s a force we sometimes cannot see –
friction.

7. FREE-BODY DIAGRAM
Verify the magnitude and direction of the net force
and recognize which will be at rest.
1. 2.
3. A physics book at rest on a horizontal tabletop
follows the law of Inertia.

8. 4. Describe the effect of net force on the motion of
the puck below.

9. Newton’s 2
nd
Law
If the net external force acts on
a body, the body accelerates. The
direction of acceleration is the
same as the direction of the net
force. The mass of the body times
the acceleration of the body
equals the net force vector.

10. Newton’s 2
nd
Lawproves that different masses
accelerate to the earth at the same rate, but with
different forces.
•We know that objects
with different masses
accelerate to the
ground at the same
rate.
•However, because of
the 2
nd
Law we know
that they don’t hit the
ground with the same
force.
F = ma
98 N = 10 kg x 9.8 m/s/s
F = ma
9.8 N = 1 kg x 9.8 m/s/s

11. If a girl slaps you, what would be your
reaction?
If a guy courts you, what would your
reaction?
Answer the following
question:

12. Newton’s 3
rd
Law
IfbodyAexertsaforceon
bodyB(an“action”),thenbodyB
exertsaforceonbodyA(a
“reaction”).Thesetwoforceshave
thesamemagnitudebutare
oppositeindirection.Theseforces
actondifferentbodies.

13. Newton’s 3rd Law in Nature
•Consider the propulsion
of a fish through the
water. A fish uses its fins
to push water backwards.
In turn, the water reacts
by pushing the fish
forwards, propelling the
fish through the water.
•The size of the force on
the water equals the size
of the force on the fish;
the direction of the force
on the water (backwards)
is opposite the direction
of the force on the fish
(forwards).

14. 3
rd
Law
The reaction of a rocket is
an application of the third
law of motion. Various
fuels are burned in the
engine, producing hot
gases.
The hot gases push against
the inside tube of the rocket
and escape out the bottom
of the tube. As the gases
move downward, the rocket
moves in the opposite
direction.

15. LETS TRY!
Example#1:
Howmuchinertiawoulda50kgmotherhave
comparedtoher25kgchild?
a.Relatemasstoinertia.
b.Whoismoreinert?
Example #2:
Wherewoulditbeeasiertolifta2kgbagofrice–on
earthorthemoon?Why?

16. LETS TRY!
Example#3:
A force of 360 N [East] was applied by a student on a
box with a mass of 50 kg. What is the acceleration of
the box if a frictional force of 340 N acts in the
opposite direction?
Example#4:
Estimatethenetforceneededtoacceleratea1000-
kgat½g.
Example#5:
Ifa70kgskateracteduponbyanunbalancedforce
of161N[West],whatisitsacceleration?