Download Chapter 1 Forces and Pressure

FORCES AND PRESSURE
I. Laws of Motion
A. Law of Inertia
B. Law of ______________
C. Law of _____________
All introduced by Sir Isaac Newton
II. Force and Motion ( 1-1 pgs 22-30)
Speed, Velocity, Acceleration and Motion
A. SPEED
 Tells you how fast an object is moving
Distance
d
Speed = -------------- = ---Time
t
EX: If you travel 130 miles in 2 hours, what was your average speed?
Formula:
Substitution:
Answer and Label:
Speed =
d
t
B. VELOCITY
 Tells you how fast and in what direction
an object is moving.
d
Velocity = -------------- = ---- direction
Distance
Time
t
EX: What is your velocity if it takes you 25 hours to drive 1,000
miles to Orlando, Florida?
Formula:
Velocity =
d
t
Substitution:
Answer and label:
C. ACCELERATION:



speeding up
slowing down
a change in direction
change in velocity
v
Acceleration = -------------- = ---Time
t
direction
EX: If a car goes from 0 mph to 60 mph in 10 seconds,
what is its’ acceleration?
Formula: A =
v
t
Substitution:
Answer and Label:
Practice- remember: Formula, substitution, labeled answer.
TRY:
If you travel 160 miles and it takes you 4 hours,
what is your speed?
TRY: If you travel 3,500 miles to Disneyland in California
And it takes you 50 hours, what is your velocity?
TRY: If you accelerate to pass a car and your speed goes
from 50 to 70 miles per hour in 5 seconds, what is
your acceleration?
TRY: If you travel 90 miles to Canada and it takes you 1.5
hours, what is your velocity?
D. INERTIA (Idle or lazy)
 The tendency of an object to resist changes
in motion.
 Objects seem _________ because they do
not easily change the way they __________.
 Objects at rest don’t want to start ________,
objects moving do not want to ___________.
1. MASS (effects on inertia)
Q. Is it easier to move a large truck or a small car?
Therefore: the more mass you have the greater
the inertia.
TRY: Which has greater inertia?
a) A pillow or a toaster?
b) A balloon or a brick?
c) A desk or a chair?
d) A refrigerator or a stove?
E. NEWTON’S FIRST LAW OF MOTION
 An object will remain at rest and an object in motion
will remain in motion at a constant velocity
UNLESS
it is acted on by an outside force.
 A force is a push or pull on matter.
1. Interactions that push or pull
A.
FRICTION
o A force that resists motion between two objects in
contact with each other.
Q: What might be some important aspects of friction?
B.
GRAVITY
o A force of attraction between any two objects
caused by their masses.
o As the mass _________, so does the __________.
o All objects accelerate towards earth at the rate of
9.8 m2 unless acted upon by air resistance.
s
EXTRA: A feather would fall as fast as an elephant
IF
there was no air resistance!!!!
III. 1-2 How forces act on objects (pg. 31-38)
A. NEWTON’S SECOND LAW OF MOTION:Momentum
1. Formula:
Force = Mass ● Acceleration
 This means a force causes a mass to accelerate
 If the mass is large, you will need a large force to move
it
 If you want to accelerate quickly, you will need a larger
force
Law of Momentum:
F=M●A
Units used: 1.
2.
Mass
kg
Acceleration
m
s2
3. Force
kg/m/s/s
also called a
NEWTON (N)
EX: What amount of force would have to be applied to
a 15 kg mass to accelerate it 6 m2 ?
s
Formula: F = m ● a
Substitution:
In class activity
Mr. King
1. What is the force required causing an acceleration
of 16
m
in a 4 kg mass?
s2
2. What is there force required to cause an acceleration
of 7
m
in an 18 kg mass?
s2
3. A force of 30 N is exerted on a 5 kg mass. What is the
object’s acceleration?
4. A force of 40 N is applied to a mass and causes an acceletration
of 8
m
. What is the object’s mass?
s2
5. What is the weight of a 10 kg mass?
6. How much force must you exert to hold a 10 kg mass at one
height?
B. NEWTON’S THIRD LAW OF MOTION:
 For every ACTION FORCE there is an equal and
opposite REACTION FORCE.
1. ACTION FORCE - a push or pull on matter
2. REACTION FORCE – the force that pushes back on
you at the exact moment.
EX: rocket
Balanced Force:
 When the force on one side of an object is equal to the
force on the other side of the object.
 There will be NO acceleration.
EX: book
Unbalanced Force
 When the forces acting upon an object are not equal
 There WILL be acceleration…a change in motion
Weight
 The gravitational force acting on an object
 Falling objects accelerate at the rate of 9.8
m
s2
Momentum

Momentum =
M●V
 When the mass is large, momentum is ____________
 When the velocity is large, momentum is ___________
EX: Shooting a bullet vs throwing a bullet
Concept Map of the Laws!!!!
Newton’s Laws of Motion
Homework: Newton’s Laws
Name ______________
Identify which of Newton’s Laws of Motion each of the
following is the BEST example of. Write either: I, II, or III.
_____ 1. The Voyager satellite needed no fuel supply to
CONTINUE MOVING past Uranus after it left Earth.
_____ 2. Using the SAME BAT a baseball player can hit a
baseball further than a softball.
_____ 3. You must use MORE FORCE to move a sled with
someone on it than when it is empty.
_____ 4. Pulling BACK on the oars moves a boat FORWARD.
_____ 5. The EXHAUST of a jet engine move the airplane
FORWARD.
_____ 6. You are thrown in to the door when a car
CHANGES DIRECTION.
_____ 7. Which law explains the action occurring in the
diagram below:
_____ 8. Which of Newton’s Laws explains why the
skateboard doesn’t go with the skater when he
pushes off?
1-3 Pressure and Buoyancy (p. 39-45)
Pressure- the weight or force acting on each unit of area
Pressure = Force
Area
Ex: How much pressure does 80N of force
exert on 5 cm2?
It is different with fluids--- the pressure exerted by a fluid
depends on the height of the column of water above the
object.
Shallow water can not exert much pressure on you because
there is not much water above you.
The deeper you dive in water the taller the column of water
above….thus the more pressure it exerts on you.
Why you float…….
When you get into water you displace water (move the
water out of the way) the volume of the water displaced is
equal to the volume of the object that is submerged.
Archimedes – Greek mathematician discovered in the 3rd
century the following concept….
“the weight of water displaced by an object is equal to
the amount of weight lost by the object”
In other words, big objects displace a lot of water AND
water weighs a lot…..so the more water you displace, the
more weight you will reduce in the water.
Another concept….
If you “lose” 25 pounds while you are in a pool, it is because
water is also pushing up on you with a force of 25 pounds.
This force is called….
Buoyant Force—upward force exerted by water (or any
other fluid) that is equal to the weight of the water the
object is displacing.
In- class worksheet
Pressure
1. How much pressure does 80N of force exert on an area
of 16cm2?
2. How much pressure does 120N of force exert on an
area of 12 cm2?
3. How much pressure does 450N of force exert on an
area of 100cm2?
4. An elephant applies a pressure of 60N/cm2 and uses a
total surface area of 500cm2. Calculate the force the
elephant needed to exert this kind of pressure?