Download 4/13/15 and 4/14/15 AIM: Define and apply Newton`s Second Law of

4/13/15 and 4/14/15
AIM: Define and apply Newton’s Second Law of Motion
* Welcome Back!
First, I will give back and go over the Ch. 2 Tests and then we will
start Chapter 3...
** DISCUSSION...
Scenario - A pitcher throws a baseball and a softball as hard
as he/she can; why don't they have the same speed?
NOTES:
1. The greater the force exerted on an object, the greater the
acceleration the object experiences (change in velocity).
2. The acceleration of an object depends on its mass as well as
the force exerted on it.
3. Newton’s Second Law of Motion states that the acceleration of
an object is in the same direction as the net force on the object,
and that the acceleration can be calculated from the following
equation:
i. a = Fnet/m
ii. Fnet = ma
iii.m = Fnet/a
iv. You can use the formula circle here!
* Do the Applying Math Box on page 69 for practice: Q. 1 – 3
FYI - One newton (N) = 1 kg x m/s 2
1.
2.
3.
4/15/15
AIM: Describe the 3 different types of friction
DO NOW: Copy down the following NOTES 1. Friction is the force that opposes the sliding motion of two surfaces
that are touching each other.
2. The force of friction between two objects in contact depends on the kinds
of surfaces and the force pressing them together
3. The three kinds of friction are:
a) static friction – the frictional force that prevents two surfaces from
sliding past each other
b) sliding friction – the force that opposes the motion of two surfaces
sliding past each other
c) rolling friction – is the frictional force between a rolling object and
the surface it rolls on.
Sliding Friction
Static Friction
Rolling Friction
4. The word friction comes from the Latin word fricare, which
means “to rub.”
5. If two surfaces are in contact, welding or sticking occurs
where the bumps (microwelds) touch each other.
* These microwelds are the source of friction.
4/16/15
* Same AIM...YAY FOR SCIENCE :)
6. The larger the force pushing the two surfaces together is,
the stronger these microwelds will be, because more of the
surface bumps will come into contact.
7. To move one surface over the other, a force must be
applied to break the microwelds.
8. Air resistance opposes the motion of objects that move
through the air because it acts in the opposite direction as the
object.
9. The size of the resistance force depends on the speed, size,
and shape of an object.
* Finally, the upward air resistance force becomes large enough to balance the
downward force of gravity.This means the net force on the object is zero.
Then the acceleration of the object is also zero, and the object falls with a
constant speed called the terminal velocity.
10. Terminal velocity is the highest speed a falling object will reach.
11. The terminal velocity depends on the size, shape, and mass of a
falling object.
Practice Problems 1. A 1650 kg car accelerates at a rate of 4.0 m/s2 . How much force is the car’s engine
producing?
2. A 68 kg runner exerts a force of 59 N. What is the acceleration of the runner?
3. A crate is dragged across an ice-covered lake. The box accelerates at 0.08 m/s2 and
is pulled by a 47 N force. What is the mass of the box?
* Newton's 2nd Law of Motion Handout!
AIM: Describe the gravitational force
NOTES:
1. Gravity is an attractive force between any two objects that
depends on the masses of the objects and the distance between
them.
2. This force increases as the mass of either of the objects
increases or moves closer.
3. The four basic forces are: gravity, electromagnetic force,
the strong nuclear force, and the weak nuclear force.
a. The two nuclear forces act only on particles in the nuclei of
atoms.
b. Electricity and magnetism are caused by the electromagnetic
force.
c. Chemical interactions between atoms and molecules also are
due to the electromagnetic force.
The Law of Universal Gravitation:
(G = 6.67 x 10-11m3/kg*s2)
* You do not have to do math with this formula, but you must
recognize what this formula is!
FUN FACT:
In the 1840s the most distant planet known was Uranus.
The motion of Uranus calculated from the law of universal gravitation
disagreed slightly with its observed motion.
Some astronomers suggested that there must be an undiscovered planet
affecting the motion of Uranus.
Using the law of universal gravitation and Newton’s laws of motion, two
astronomers independently calculated the orbit of this planet.
As a result of these calculations using gravitational, the planet Neptune was
found in 1846.
4. No matter how far two objects are apart, the gravitational
force between them never completely goes to zero.
a. Because of this, gravity is called a long-range force.
5. Earth’s Gravitational Acceleration – when all forces except
gravity acting on a falling object can be ignored, the object is said
to be in free fall.
a. Close to the Earth’s surface, the acceleration of a falling
object in free fall is about 9.8 m/s2.
b. You can calculate this using the formula:
F = mg (see discussion regarding weight formula!)
* You can use the circle formula here!
4/20/15
AIM: Ch. 3 Vocabulary Quiz
* When you are finished, hand in your quiz on the SMART Board Cover,
then complete the CPR Course Evaluation. Once you've completed that,
you may pick up your HW Handout.
4/21/15
AIM: Distinguish between mass and weight
DO NOW: * Take out your HW - do NOT pass up!
* Copy down the following NOTES 1. The Earth is exerting a gravitational force on you at all times.
a. Weight is the gravitational force exerted on an object.
2. Because the weight of an object on Earth is equal to the force of
Earth’s gravity on the object, weight can be calculated from this
equation:
* You can use the formula circle here!
* On Earth, g = 9.8 m/s2
* Unless noted otherwise,
always use g = 9.8 m/s2
3. Weight and mass are not the same!
4. Weight is a force and mass is a measure of the amount of
matter an object contains.
5. However, they are related. As mass increases, weight increases.
* LOOK AT TABLE 1 – weight on different planets...
* The table shows how various weights on Earth would be
different on the Moon and some of the planets.
4/22/15
* Same AIM...
DO NOW:
* Take out Monday's HW and last night's HW - do NOT pass up!
(it's the SAME Handout...in case you forgot)
6.
Floating in Space – free fall – less force is exerted!
a. Objects are weightless in free fall!
DISCUSSION * When you stand on a scale you are at rest and the net force on you is
zero.The scale supports you and balances your weight by exerting an upward
force. The dial on the scale shows the upward force exerted by the scale,
which is your weight.
* Now suppose you stand on the scale in an elevator that is falling. If you and
the scale were in free fall, then you no longer would push down on the scale at
all.The scale dial would say you have zero weight, even though the force of
gravity on you hasn’t changed.
DISCUSSION So what does it mean to say that something is weightless in orbit?
A space shuttle in orbit is in free fall, but it is falling around Earth,
rather than straight downward. Everything in the orbiting space
shuttle is falling around Earth at the same rate, in the same way you
and the scale were falling in the elevator. Objects in the shuttle seem
to be floating because they are all falling with the same acceleration.
4/23/15
* Same AIM...
DO NOW: Work on these 3 practice problems.
* Assume all objects are on Earth...
1. A locomotive’s mass is 18,181.81 kg. What is its weight?
2. A small car weighs 10168.25 N. What is its mass?
3. What is the weight of an infant whose mass is 1.76 kg?
AIM: Explain why objects that are thrown will follow a curved path
DO NOW: Answer the following question...
1. What word refers to anything thrown or shot through the air?
ANSWER 1. projectile
NOTES:
1. Earth’s gravity causes projectiles to follow a curved path.
2. Horizontal and vertical motions are independent of one
another.
3. Horizontal motion results from the force of one thing on
another.
4. Vertical motion results from the downward force of gravity.
5. However, a ball thrown and a ball dropped (from the same
height) (therefore, experiencing horizontal and vertical motion) will
hit the ground at the same time.
6. Look at Figure 17 on p. 80
7. Acceleration toward a curved or circular path is called
centripetal acceleration.
a. As a result, the net force must also be directed toward the
center of a curved path (centripetal force).
i. Look at p. 81 Centripetal Force and Traction
8. Gravity exerts a centripetal force on the Moon that keeps it
moving in nearly a circular orbit.
Centripetal Force
* Practice Problem 1. A little boy is pulling a wagon with his dog in it. The mass of the
dog and wagon together is 45 kg. The wagon accelerates at a rate
of 0.85 m/s2. What force is the boy pulling with?
* Additional Practice Problems on a separate file...
(if time permits)
4/27/15
AIM: Explain Newton’s 3rd Law of Motion to identify action and
reaction forces
DO NOW: Copy down the following NOTES 1. Newton’s Third Law of Motion describes action-reaction pairs:
when one object exerts a force on a second object, the second one
exerts a force on the first that is equal in strength and opposite in
direction.
* To every action force there is an equal and opposite reaction
force.
2. Action and Reaction forces do not cancel because they are
acting on different objects.
a. What are some examples of this?
- Trampoline, Diving Board, Bouncing Castle, Skating Couple,
Swimmer, Rocket Propulsion
AIM: Calculate momentum and recognize when momentum is conserved
NOTES:
1. Momentum is the product of an object’s mass and velocity given by
the following formula:
a. You can use the formula circle here!
2. The unit for momentum is kg x m/s.
* The net force exerted on an object can be calculated by
dividing its changes in momentum by the time over which the
change occurs. (The force depends on the mass and the initial
velocity of the ball, and how long it takes the ball to stop.)
F = (mv f - mv i) / t
3. Law of Conservation of Momentum – Momentum can be
transferred from one object to another – discussion billiards
game!
a. If a group of objects exerts forces only on each other,
their total momentum does not change.
4. When Objects Collide p. 88
a. What are some examples of this?
- Billiards, Newton’s Cradle, Bowling Ball and Pins
Momentum Transfer
ZERO Momentum
Ch. 3 Formula Sheet
F
Fnet = mass x acceleration
m
a
F
m
g
W
m
weight = mass x acceleration
of gravity
g
p
m
Fnet = mass x acceleration
of gravity
momentum = mass x velocity
v
4/30/15
AIM: Ch. 3 Review
5/1/15
AIM: Ch. 3 Test