newton laws

1
(No Transcript)
2
Newton s laws of motion
3
Sir Isaac Newton (1642 1727)

• Worked out the three laws of motion governing
  the movement of all objects at all times an in
  all circumstances.
• He published them in his book Philosophiae
  Naturalis Principia Mathematica (mathematic
  principles of natural philosophy) in 1687.

4
If I have ever made any valuable discoveries,
it has been owing more to patient attention, than
to any other talent. -Sir Isaac Newton
5
Newtons First Law
An object at rest tends to stay at rest and an
object in motion tends to stay in motion unless
acted upon by an unbalanced force.
6
Newtons 1st Law of Motion
7
What does this mean?

• Basically, an object will keep doing what it was
  doing unless acted on by an unbalanced force.
• If the object was sitting still, it will remain
  stationary. If it was moving at a constant
  velocity, it will keep moving.
• It takes force to change the motion of an object.

8
What is meant by unbalanced force?
If the forces on an object are equal and
opposite, they are said to be balanced, and the
object experiences no change in motion. If they
are not equal and opposite, then the forces are
unbalanced and the motion of the object changes.
9
Some Examples from Real Life
A soccer ball is sitting at rest. It takes an
unbalanced force of a kick to change its motion.

• Two teams are playing tug of war. They are both
  exerting equal force on the rope in opposite
  directions. This balanced force results in no
  change of motion.

10
1st Law

• THE COIN WOULD BE IN REST UNLESS ACTED UPON BY AN
  UNBALANCED FORCE

11
1st Law

• Once airborne, unless acted on by an unbalanced
  force (gravity and air fluid friction), it
  would never stop!

12
Why was it so difficult to stop the TITANIC from
colliding with the iceberg?
13
The mass of the Titanic is very large.
Inertia is proportionate to mass.
The Titanic could not change its direction
because its extremely high inertia forces it to
continue in a straight line, thereby colliding
with the iceberg.
menu
14
Newtons Second Law
The acceleration of an object is directly
proportional to the net force acting on it and
inversely proportional to its mass.
15
What does F ma mean?

• Force is directly proportional to mass and
  acceleration. Imagine a ball of a certain mass
  moving at a certain acceleration. This ball has
  a certain force.

Now imagine we make the ball twice as big (double
the mass) but keep the acceleration constant. F
ma says that this new ball has twice the force
of the old ball.
Now imagine the original ball moving at twice the
original acceleration. F ma says that the ball
will again have twice the force of the ball at
the original acceleration.
16
More about F ma

• If you double the mass, you double the force. If
  you double the acceleration, you double the
  force.
• What if you double the mass and the acceleration?
• (2m)(2a) 4F
• Doubling the mass and the acceleration quadruples
  the force.
• So . . . what if you decrease the mass by half?
  How much force would the object have now?

17
What does F ma say?
F ma basically means that the force of an
object comes from its mass and its acceleration.
Something very massive (high mass) thats
changing speed very slowly (low acceleration),
like a glacier, can still have great force.
Something very small (low mass) thats changing
speed very quickly (high acceleration), like a
bullet, can still have a great force. Something
very small changing speed very slowly will have a
very weak force.
18
What is the function of the hand glove of this
baseball player?
19
F ma m
(v-u)
t
Force is inversely proportional to time
The hand glove increases the time of the
collision, thereby reducing the force.
menu
20
Check Your Understanding

• 1. What acceleration will result when a 12 N net
  force applied to a 3 kg object? A 6 kg object?
•  
• 2. A net force of 16 N causes a mass to
  accelerate at a rate of 5 m/s2. Determine the
  mass.
• 3. How much force is needed to accelerate a 66 kg
  skier 1 m/sec/sec?

21
Check Your Understanding

• 1. What acceleration will result when a 12 N net
  force applied to a 3 kg object?
• 12 N 3 kg x 4 m/s/s
•  
• 2. A net force of 16 N causes a mass to
  accelerate at a rate of 5 m/s2. Determine the
  mass.
• 
  16 N 3.2 kg x 5 m/s/s
•  
• 3. How much force is needed to accelerate a 66 kg
  skier 1 m/sec/sec?
• 66 kg-m/sec/sec or 66 N

22
Newtons Third Law

• For every action there is an equal and opposite
  reaction.

23
3rd Law

• According to Newton, whenever objects A and B
  interact with each other, they exert forces upon
  each other. When you sit in your chair, your body
  exerts a downward force on the chair and the
  chair exerts an upward force on your body.

24
3rd Law

• There are two forces resulting from this
  interaction - a force on the chair and a force on
  your body. These two forces are called action and
  reaction forces.

25
3rd Law
Flying gracefully through the air, birds depend
on Newtons third law of motion. As the birds
push down on the air with their wings, the air
pushes their wings up and gives them lift.
Reaction
Force
26
3rd 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.
27
Presented by