Transcript ForceCh2PowerPointup..

Motion and Forces
Chapter 2
Bell Work 1/21/10
Copy each of these statements onto your
bell work sheet. Then decide if they
are true or false. If false correct them.
1. Speed includes direction, while velocity
does not.
2. A moving object covers the same distance
in less time if its velocity is greater.
3. Acceleration measures only change in
speed.
Bell Work 1/22/10
Please begin working on your
foldable or PowerPoint
On your bell work sheet write
down “working on project” for
today
Bell Work 1/25/10
Please begin completing the
Map Practice Packet. Write
your answers for each
question on your yellow bell
work sheet for today.
PLEASE DO NOT WRITE IN
THE PACKET
Force 2.1 Notes
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forces occur when
one object pushes
or pulls on another
object
We say that one
object exerts a force
on another object to
cause it to
accelerate.
Describing Forces
 forces
are
describe
according to:
strength and
 direction
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Two types of Forces
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Unbalanced Force
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two forces acting in the
same direction
OR
One stronger force
acting in the opposite
direction of a weaker
force.
*Unbalanced forces
cause an object to
accelerate!
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Balanced Force

equal forces acting in
opposite directions
* balanced forces will NOT
change the object’s
motion!
Newton’s First Law
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An object at rest will
remain at rest unless
acted upon by an
unbalanced force!
continued

An object moving at
constant velocity will
continue moving at
constant velocity unless
acted upon by an
unbalanced force.
Inertia Lab Questions
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Before you start this experiment, see if you can decide which egg is the raw one and which
egg is the hard boiled one. Place the eggs on the two plates and start them spinning at the
same time. The egg that continues spinning for the longest time is the hard boiled egg.
Steps for the 1st experiment:
1. Place the uncooked egg on a plate and start it spinning.
2. Touch it lightly with your fingertip to stop the egg spinning.
3. Once the egg stops take your finger away immediately.
What happens to the egg? The shell of the egg actually stops spinning but the inside (yolk
and egg white) keeps spinning. Because the inside of the raw egg is a liquid, it makes the
egg start to spin again. This force is called inertia.
Steps for the 2nd experiment:
1. Place the hard-boiled egg on a plate and start it spinning.
2. Touch it lightly with your fingertip to stop the egg spinning.
3. Once the egg stops take your finger away immediately.
What happens to the egg? The boiled egg stops spinning because the inside contents of
the egg are a solid mass.
Steps for the 3rd experiment:
1. Place both eggs on the plates (one on each plate).
2. Start both eggs spinning at the same time.
3. Place your finger on each egg at the same time to quickly stop them spinning.
4. Let go of both eggs at the same time.
Now you can compare how the hard-boiled egg stops spinning and the raw egg keeps
spinning.
Law of Inertia
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Newton’s first law is often
referred to as the Law of
Inertia.
Inertia is a property that
describes an object’s
resistance to changes in
motion.
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if an object is moving,
inertia keeps it moving.
if an object is at rest, inertia
keeps it at rest.
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Mass – is the amount of
matter in an object.
Mass is a measure of
inertia.
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the more mass an object
has the more inertia it has.
This means it will take more
force to get it to accelerate.
the opposite is also true:
less mass, less inertia, less
force.
mass is measured in kg.
How are mass and inertia
related?
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The more matter
in an object, the
harder it is to get
the object to
accelerate or you
could say the
harder it is to
overcome the
object’s inertia.
Bell Work 1/26/10
Please answer #1-4 on
page 47 in the book on
your yellow bell work
sheet.
Force 2.2 Notes
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Newton’s Second Law of
Motion
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Explains a relationship
between force, mass and
acceleration
Often expressed as:
force =
mass x acceleration
Simply stated: An object’s
acceleration depends on the
mass of an object and the
strength and direction of the
force acting on it.
Force = mass x acceleration
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Units:
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acceleration – m/s/s
mass – kg
force – kg x m/s/s or
Newton (N)
Rearranging the Force
Equation
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To calculate mass:
Mass = ___force___
acceleration
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To calculate
acceleration:
Acceleration = force
mass
Using the formula
acceleration = force/mass
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We know the following:
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as force increases,
acceleration increases.
as mass increases,
acceleration decreases.
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to get an object to
accelerate, you must
increase force or
decrease mass.
Bell Work 1/27/10 – choose the correct word
to fill in the blanks: force, inertia, motion, net
force, Newton’s first law, unbalanced force
1.
2.
3.
4.
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6.
_______ is the change of position over time.
The overall force acting on an object when all forces are
combined is called _____
A force that can change the motion of an object is called
a(n) ________.
A(n) _______ is a push or a pull.
Objects at rest remain at rest, and objects in motion
remain in motion at the same velocity, unless acted on by
an unbalanced force. This statement describes ____.
The resistance of an object to a change in speed or
direction is called_______.
Bell Work 1/28/10
Fill in the blanks
1.
2.
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4.
If you increase the force on a box, it will have
_______ inertia.
You push two chairs in a straight line with the
same force. One chair is more massive than the
other. The more massive chair will have
_______ acceleration.
Any force that is keeping an object moving in a
circle is known as ______.
Acceleration is ________.
force – any force
that keeps an object moving
in a circle
 Centripetal
Force Notes 2.3
Newton’s Third Law – states
that for every action there is a
reaction
Bell Work 2/2/10 – Please get a
new green bell work sheet!
1.
2.
3.
Identify the action/reaction force pair
involved when you catch a ball.
Explain the difference between balanced
forces and action/reaction forces.
A man pushes on a wall with a force of
50 N. What are the size and the direction
of the force that the wall exerts on the
man?
Bell Work 2/4/10 – Look back in
your notes for the formulas or in
the book pg 51-53
1. A model rocket is accelerating a 6 m/s2.
The force on it is 2 N. What is the mass
of the rocket?
2. Another model rocket that has a mass
of 15 kg is accelerating at 5 m/s2. What
is the force being applied to the rocket?
3. A girl pushes a 10 kg shopping cart with
a force of 30 N. What is the
acceleration of the cart?
Force 2.4 Notes
Objects in motion have momentum. Which would
have more momentum a bowling ball being
thrown at a wall or a tennis ball?
Momentum – A measure of mass in motion. The
momentum of an object is the product of its mass
and velocity
Formula to calculate momentum
Momentum = mass x velocity
p = mv
Momentum Calculations
Example 1 - What is the momentum of a 1.5 kg ball
moving at 2 m/s?
Example 2 – A 6 kg ball is moving with a velocity of
2 m/s. What is the ball’s momentum?
Example 3 – What is the momentum of a 0.5 kg ball
moving at 0.5 m/s?
• Momentum is a property of a
moving object.
momentum
Momentum can be transferred
from one object to another
If two objects involved in a collision have very
different masses, the one with the less mass
has a greater change in velocity.
Collision – a situation in which two objects in
close contact exchange energy and
momentum
What happens with 2 bumper cars?
Forces in collisions are equal
and opposite.
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forces in collision
Momentum is conserved
Conservation of momentum – states that the
total momentum of a system of objects does
not change, as long as no outside forces are
acting on that system.
• Momentum is conserved in
collisions.
total momentum
momentum 1
momentum 2
Bell Work – 2/5/10
Complete # 11-16 on page 71.
You only have to write the
letter of the answer.