Newtons laws of motion

While most people know what Newton's laws say, many people do not know what they mean (or simply do not believe what they mean).

1. Previous Lesson (Chapter 4)Previous Lesson (Chapter 4)
Average acceleration = Average acceleration = Change of the velocityChange of the velocity
Time taken for the changeTime taken for the change
a = a = v – u v – u (unit : (unit : m/m/s
2
))
tt
where, a = accelerationwhere, a = acceleration
u = initial velocityu = initial velocity
v = final velocityv = final velocity
t = time t = time

2. Newton’s Newton’s
Laws of Laws of
MotionMotion
I.I. Law of Inertia Law of Inertia
II.II. F=ma F=ma
III.III. Action-Reaction Action-Reaction

3. While most people know While most people know
what Newton's laws say, what Newton's laws say,
many people do not know many people do not know
what they mean (or simply do what they mean (or simply do
not believe what they mean). not believe what they mean).

4. ObjectivesObjectives

To define force and inertia.To define force and inertia.

To state Newton’s three laws of motion.To state Newton’s three laws of motion.

To perform calculations involving force, To perform calculations involving force,
F=ma.F=ma.

5. ForceForce
In general, force can be defined as the effects of In general, force can be defined as the effects of
pushing or pulling an object to :pushing or pulling an object to :
i)i)cause a change in the motion of an object, cause a change in the motion of an object,
or/andor/and
ii)ii)cause a change in the shape of an object.cause a change in the shape of an object.

7. InertiaInertia

Inertia is the tendency of an object to Inertia is the tendency of an object to
resist changes in its motion.resist changes in its motion.

Amount of Inertia depends on the mass of Amount of Inertia depends on the mass of
the object. A the object. A larger mass larger mass has a has a larger larger
InertiaInertia while a while a smaller mass smaller mass has a has a
smaller Inertiasmaller Inertia

8. 11
stst
Law of Motion Law of Motion
(Law of Inertia) (Law of Inertia)
““An object remains in a state An object remains in a state
of rest, or continues in a state of rest, or continues in a state
of uniform motion in a of uniform motion in a
straight line, unless it is acted straight line, unless it is acted
on by an externally force.”on by an externally force.”

9. 11
stst
Law Law
These pumpkins will not move unless acted on
by an external force.

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

11. 22
ndnd
Law of Motion Law of Motion

12. 22
ndnd
Law Law
““The acceleration of an object The acceleration of an object
acted upon by an external force is acted upon by an external force is
proportional to the force and is in proportional to the force and is in
the direction as the force.”the direction as the force.”

13. 22
ndnd
Law Law

When mass is in kilograms and acceleration is When mass is in kilograms and acceleration is
in m/in m/s
2
, the unit of force is in newtons (N)., the unit of force is in newtons (N).

One newton is equal to the force required to One newton is equal to the force required to
accelerate one kilogram of mass at one accelerate one kilogram of mass at one
meter/second/second.meter/second/second.

14. Check Your UnderstandingCheck Your Understanding

1. What acceleration will result when a 12 N net force applied to a 3 kg 1. What acceleration will result when a 12 N net force applied to a 3 kg
object? A 6 kg object?object? A 6 kg object?


2. Calculate the force needed to accelerate a boat of mass 20 tonne 2. Calculate the force needed to accelerate a boat of mass 20 tonne
uniformly from rest to a speed of 21.6 km/h in 10 minutes?uniformly from rest to a speed of 21.6 km/h in 10 minutes?

15. 33
rdrd
Law of Motion Law of Motion
““For every action force, there is For every action force, there is
an equal and opposite reaction an equal and opposite reaction
force.”force.”
F
Action
= - F
Reaction

16. Other examples of Newton’s Other examples of Newton’s
Third LawThird Law

17. 33
rdrd
Law Law

18. 33
rdrd
Law Law