Download speed

What is Motion?
Motion: A change in position of an
object compared to a reference point
Motion involves all of the following:
What is Motion?
Speed
The rate of change in position
Speed = distance ÷ time or
= distance
time
What is Motion?
Velocity
Speed plus direction
Example: 50 km/hour north
What is Motion?
Acceleration
The rate of change in velocity
Positive acceleration = speeding up
Negative acceleration = slowing down (decelerate)
Acceleration = Vfinal – Vinitial
Time
or = ∆Velocity
Time
Motion Questions
1) What units are used to measure
speed?
2) What units are used to measure
acceleration?
3) What is another way to say
“slowing down” in terms of
acceleration?
Answer this in the “In” for Forces
• Name 3 forces off the top of your head.
What is a Force?
FORCE = Any push or pull which causes
something to move or change its speed
or direction
What is a Force?
Forces can be BALANCED or UNBALANCED
Balanced forces are equal in size and
opposite in direction
Arrow thickness is equal.
Net Force = 0.
Balanced forces result in no
movement.
What is a Force?
Forces can be BALANCED or UNBALANCED
Unbalanced forces in the same direction
Arrow thickness is not
equal.
Net Force =
When two forces act in the same direction,
the net force is the sum of the two individual
forces. Box moves right
What is a Force?
Forces can be BALANCED or UNBALANCED
Unbalanced forces are not equal in size
and/or opposite in direction. If the forces
on an object are UNBALANCED, we say a
NET force results.
Net force =
Box moves right.
“Out” Force Questions
1) What famous physicist are units of
force named after?
2) If Moby has a mass of 50 kg and
Tim has a mass of 40 kg, who would
require more force to move?
Gravity and Friction
• New Cornell notes (in, out, through) for
gravity and friction.
In For Gravity and Friction
• Does a person have gravity?
What is Gravity?
GRAVITY: An attraction force between all
masses
Newton’s universal law of gravitation:
Every object in the universe exerts a
gravitational attraction to all other
objects in the universe
The amount of gravitational force
depends upon the mass of the objects
and the distance between the objects
What is Gravity?
The greater the mass, the greater the
force
The greater the distance, the less the
force
Acceleration due to gravity = 9.8 m/s/s
or 9.8 m/s2
What is Weight?
Weight is a measure of the gravitational
force between two objects
The greater the mass the greater the
force (weight)
Measured in units called Newtons (N)
In the standard system units are
pounds (lbs)
“Out” Gravity Questions
1) How does the gravity on the
moon compare to the gravity on
Earth?
2) Why don’t you notice your own
gravitational pull on the Earth?
3) On what two things does the
force of gravity depend?
What is Friction?
Friction = A force that opposes or slows
down motion
Caused by the physical contact
between moving surfaces
The amount of friction depends upon 2
things: 1.) kinds of surfaces and 2.)
force pressing the surfaces together
Changes motion into heat
What is Friction?
4 Types of Friction:
1. Rolling Friction (bike tire on the road)
2. Sliding Friction (book sliding on table)
3. Fluid Friction (object moving through
air or water)
4. Static Friction (force holding things
still)
Air resistance:
The force of air exerted on a
falling object
 The air pushes up as gravity pulls down
 Dependent upon the shape and surface area
of the object
 When the air resistance equals the force of
gravity, terminal velocity is reached
 Terminal velocity is the highest velocity that
an object will reach as it falls
The feather reaches terminal
velocity quickly. Air resistance and
gravity cancel each other out so
the feather stops accelerating. The
elephant keeps accelerating due to
its shape, surface area and mass.
An Elephant and a Feather both
fall at the same rate when air is
removed (vacuum).
Apollo astronauts dropped a
feather and a hammer during their
lunar experiments. Both landed at
the same time.
Examples of Friction?
What are some ways athletes use friction?
Friction and Gravity “Out” Activity.
First Law: An object at rest stays at rest or
an object in motion, stays in motion (in
the same direction/at the same speed)
unless acted upon by an unbalanced
force
Also called the law of inertia
Inertia is:
A property of matter
The tendency of an object to resist any
change in its motion
The greater the mass the greater the inertia
The greater the speed the greater the inertia
Examples of Newton’s 1st Law
a) car suddenly stops and you strain against the seat belt
b) when riding a horse, the horse suddenly stops and you
fly over its head
c) the magician pulls the tablecloth out from under a
table full of dishes
d) the difficulty of pushing a dead car
f) car turns left and you appear to slide to the right
Second law: The greater
the force applied to an
object, the more the
object will accelerate.
It takes more force to
accelerate an object
with a lot of mass than
to accelerate
something with very
little mass.
The player in black had more
acceleration thus he hit with a
greater amount of force
Second law:
The greater the force, the greater the acceleration
The greater the mass, the greater the force needed
for the same acceleration
Calculated by: F = ma
 (F = force, m = mass, a = acceleration)
Examples of Newton’s 2nd Law
a) hitting a baseball, the harder the hit, the faster the ball
goes
b) accelerating or decelerating a car
c) The positioning of football players - massive players on
the line with lighter (faster to accelerate) players in the
backfield
d) a loaded versus an unloaded truck
Examples of Newton’s 2nd Law
The second law states that
unbalanced forces cause
objects to accelerate with an
acceleration which is directly
proportional to the net force
and inversely proportional to
the mass. This one is telling
us that big heavy objects
don’t move as fast or as
easily as smaller lighter
objects. It takes more to
slow down a charging bull
then to slow down a
charging mouse.
“In” Activity
How can climbing into a boat from a dock be used to
explain Newton’s 3rd Law?
third law: For every
action force, there is
an equal and opposite
reaction force. (Forces
are always paired)
rd
Examples of Newton’s 3 Law
a) rockets leaving earth
b) guns being fired
c) two cars hit head on
d) astronauts in space
e) pool or billiards
f) jumping out of a boat onto the dock
Examples of Newton’s 3rd Law
Examples of Newton’s 3rd Law
Momentum: The quantity of motion
 A property of moving objects
 Calculated by: P = mv
 (p = momentum, m = mass, v = velocity)
• Calculating Momentum
• Momentum Practice
Momentum: The quantity of motion
 Law of conservation of momentum: the total
amount of momentum of a group of objects
does not change unless outside forces act on
the objects
This is an Inelastic collision.
Notice how there is no
bounce.
The Diesel engine’s
momentum before the
collision is _________
The Diesel engine + the flat
car momentum after the
collision is _________.
No momentum was lost or
gained.
Newton’s Laws Out Activity
1) Why does a ball roll across a rug
and come to a stop?
2) What is a net force?
3) Give an example of Newton’s 3rd
Law: