Newtons 1st Law

1
Newtons 1st Law
INERTIA
THE LAW OF
An object at rest will remain at rest, -and- an
object in motion will stay in motion, -UNLESS- it
is acted upon by an unbalanced force.
2
Newtons 1st Law of Motion
BASICALLY
Objects resist any change to their motion!
(Objects keep on doing whatever they are doing,
unless there is an unbalanced force) This
resistance is called INERTIA.
3
Newtons 1st Law of Motion

• The car was acted upon by an outside force the
  force of the wall hitting the car.
• The person inside the car wasnt hit by the force
  of the wall, so he kept moving at the same speed
  and in the same direction.

4
Newtons 1st Law of Motion

• Explain this animation
• The truck is stopped by the force of the impact
  with the car, but the ladder continues to move at
  its original speed and in its original direction
  because of inertia.

5
Newtons 1st Law of Motion

• So, how did the tablecloth demo work?
• The cloth experienced a pulling force that caused
  it to start moving. The dishes did not have a
  direct force applied to them, so they remained in
  their places because of inertia.

6
Newtons 2nd Law
Acceleration
THE LAW OF
ACCELERATION depends on the objects MASS, and
the net FORCE acting on the object. We can also
write it mathematically Force Mass x
Acceleration
7
So, how do unbalanced forces affect an objects
motion?

• The harder you hit, the faster it goes!
• The greater the force, the greater the
  acceleration

Homerun Hit
Sacrifice Bunt
8
So, how does mass affect an objects motion?

• The fuller the cart, the slower it goes!
• The more mass, the less acceleration

Empty Cart
Full Cart
9
Newtons 2nd Law of Motion

• Force Mass x Acceleration
• Mr. Sawyers car ran out of gas. How much
  force does Mr. Sawyer need to push his 750kg car
  at an acceleration of 1 m/s2?

F m x a F 750 kg x 1 m/s2 F 750 N
1 m/s2
750 kg
10
Speed, Distance Time
Newtons 2nd Law of Motion
We can also write the formula like this
Acceleration Force Mass
Mass Force Acceleration Force Mass
x Acceleration
11
Newtons 2nd Law of Motion

• Find the golf balls acceleration.
• The putter hits the 0.05 kg golfball with a force
  of 1 N.
• The driver hits the 0.05 kg golfball with a
  force of 8 N.

12
Newtons 3rd Law
Interaction
THE LAW OF
ALL forces act in PAIRS! For every action
force, there is an equal and opposite reaction
force.
13
Newtons 3rd Law of Motion

• The mans foot exerts a backward push on the boat
  (action force), while the boat exerts a forward
  push on the man (reaction force).

A PAIR OF FORCES EQUAL FORCES, BUT IN OPPOSITE
DIRECTIONS
14
Identify the force pairs in each situation

• A person fires a rifle.

• Action Force gun pushes the bullet out at high
  speed.
• Reaction Force the bullet pushes back on the
  gun (recoil).

15
Identify the force pairs in each situation

• A space shuttle lifts off.

• Action Force engine pushes gases down out.
• Reaction Force the gases push the rocket up.
• This upward force must be stronger than gravity
  pulling down on the rocket!

16
Think about it . . .

• Why does it hurt so much when you stub your toe?
  
• When your toe exerts a force on a table, the
  table exerts an equal force back on your toe.
• The harder you hit your toe against it, the more
  force the the table exerts back on your toe (and
  the more your toe hurts).

17
Balloon Race - What happened?

• 3) The balloon pushes the air out back, the
  air pushes the balloon forward.
• 4) The more air in the balloon the greater the
  force. Newtons 2nd law of motion says that the
  greater the force, the greater the acceleration.

REACTION Force
ACTION Force