Newton’s Laws

1
Newtons Laws

• Unit 2

2
Contributors to the theory of motion
3
Aristotle

• Divided motion into two types natural and
  violent
• Natural motion- either straight up or straight
  down
• Violent motion- the result of forces that pushed
  or pulled

4
Copernicus

• Reasoned that the Earth moved around the sun

5
Galileo

• Supported Copernicus
• Force any push or pull
• Friction force that acts between materials that
  touch as the move past each other
• Argued that only when friction is present is a
  force needed to keep an object moving
• Inertia the property of a body to resist change

6
Newton

• Developed the famous laws of motion

7
Newtons First Law

• Law of Inertia
• Every object continues in a state of rest, or of
  motion in a straight line at constant speed,
  unless it is compelled to change that state by
  forces exerted upon it.

8
(No Transcript)
9
The more mass an object has, the greater its
inertia the more force it takes to change its
state of motion

• Mass is different than volume weight.
• mass a measure of the inertia an object has
• Volume a measure of space
• Weight the force of gravity on an object
• weight mass x gravity

10
The combination of all forces acting on an object
is called the net force.It is the net force that
changes an objects state of motion.
11
When an object is at rest, forces balance
produce a net force of zero. One force is
gravity. The other force is the normal force.
This means that the object is in a state of
equilibrium.
12
Felicia, a ballet dancer, has a mass of 45kg.
What is Felicias weight on Earth?What is
Felicias mass on Jupiter, where the acceleration
due to gravity is 25 m/s2?What is Felicias
weight on Jupiter?
13
A 20g sparrow flying toward a bird feeder
mistakes the pane of glass in a window for an
opening and slams into it with a force of 2N.
What is the birds acceleration?
14
A 30g arrow is shot by William Tell through an
8cm thick apple sitting on top of his sons head.
If the arrow enters the apple at 30m/s and
emerges at 25m/s in the same direction, with what
force has the apple resisted the arrow?
15
Newtons Second Law

• Force mass x acceleration

16
Force causes acceleration.To increases the
acceleration of an object, you must increase the
net force acting on it.The acceleration depends
on the mass.Acceleration is inversely
proportional to the mass.
17
Force mass x acceleration
18
Friction acts on materials that are in contact
with each other. It always acts in a direction to
oppose motion. The force of friction between
surfaces depends on the kinds of materials in
contact how much the surfaces are pressed
together.
19
Friction also occurs in liquids gases. Fluid
friction occurs as an object pushes aside the
fluid it is moving through. An example is air
resistance.When friction is present, an object
may move with a constant velocity even when an
outside force is applied to it. The friction
force just balances the applied force so the net
force is zero and no acceleration occurs.
20
Pressure force/ area of application

• The smaller the area supporting a given force,
  the greater the pressure on that surface.
• Measured in pascals (Pa)
• One Newton per square meter equals one pascal

21
(No Transcript)
22
Galileo showed that objects in free fall
accelerate equally regardless of their masses.

• A 10kg cannonball and a 1kg rock would fall with
  equal accelerations- 10 m/s.

23
When air resistance is present, a falling object
accelerates only until it reaches its terminal
speed. At terminal speed, the force of air
resistance balances the force of gravity the
net force is zeroAcceleration weight -
resistance
24
Rose is sledding down an ice-covered hill
inclined at an angle of 15 degrees to the
horizontal. If Rose and the sled have a combined
mass of 54kg, what is the force pulling them down
the hill?
25
Brian is walking through the school cafeteria but
does not realize that the person in front of him
has just spilled his glass of chocolate milk. As
Brian, who weighs 420N, steps in the milk, the
coefficient of sliding friction between Brian and
the floor is suddenly reduced to 0.040. What is
the force of sliding friction between Brian and
the slippery floor?
26
While redecorating her apartment, Kitty slowly
pushes an 82kg china cabinet across the wooden
dining room floor, which resists the motion with
a force of friction of 320N. What is the
coefficient of sliding friction between the china
cabinet and the floor?
27
At Sea World, a 900kg polar bear slides down a
wet slide inclined at an angle of 25 degrees to
the horizontal. The coefficient of friction
between the bear and the slide is 0.0500. What
frictional force impedes the bears motion down
the slide?
28
Newtons Third Law

• Whenever one object exerts a force on a second
  object, the second object exerts an equal and
  opposite force on the first object.

29
Newton realized that a force is not a thing in
itself but part of a mutual action, an
interaction, between one thing another.In
every interaction, the forces always occur in
pairs cannot exist without each other.One
force is called the action force. The other is
called the reaction force.
30
Action Object A exerts a force on Object
BReaction Object B exerts a force on Object A
31
Remember that action-reaction force pairs are
equal but opposite in strength. We must also take
mass into account. A given force exerted on a
small mass produces a greater acceleration than
the same force exerted on a large mass.
32
Newtons Third law helps us to explain how
rockets are propelled, how helicopters get their
lifting force, and how birds and airplanes fly.
33
Since action and reaction forces are equal but
opposite, why dont they cancel to zero?
34
If action reaction forces are internal to a
system, they cancel each other produce no
acceleration of the system. A force external to
the system is needed to accelerate the system.
35
Flip, an exhausted gymnast, hangs from a bar by
both arms in an effort to catch his breath. If
Flip has a mass of 65kg, what is the tension in
each of Flips arms as he hangs in place?
36
At an art auction, Whitney has acquired a
painting that now hangs from a nail on her wall.
If the painting has a mass of 12.6kg, what is the
tension in each side of the wire supporting the
painting?
37
Michelle likes to swing on a tire tied to a tree
branch in her yard. If Michelle and the tire have
a combined mass of 82.5kg, and Elwin pulls
Michelle back far enough for her to make an angle
to 30 degrees with the vertical, what is the
tension in the rope supporting Michelle and the
tire?
38
After returning home from the beach, Samantha
hangs her wet 0.20kg bathing suit in the center
of the 6m long clothesline to dry. This causes
the clothesline to sag 4cm. What is the tension
in the clothesline?
39
Brooke comes home from school and puts her books
down on the kitchen table while she goes to grab
a snack. The books have a combined weight of 25N
and the area of contact is 0.19m by 0.24m. What
pressure do the books apply on the table?
40
A full coffee mug has a mass of 0.6kg and an
empty mug has a mass of 0.3kg. If the full mug
applies a pressure of 1200Pa, what is the area
inside a circular ring of coffee left on the
table by the bottom of the mug?What is the
radius of the ring of coffee?