Download ch 3 Newtons 2nd law of motion notes

Chapter 3 – Newton’s Second Law of Motion-Force and Acceleration
The BIG IDEA- **
3.1 What is Acceleration?
Besides developing the concepts of speed and velocity, Galileo
also developed the concept of **
He found that balls rolling down inclines roll **
Also found that the speed increased by a constant amount each second
– this is called **
Acceleration – def- **
Formula: **
a= V/t
acceleration equals change in velocity divided by the change in time
( - delta symbol that always means ‘change in’)
Acceleration can be more than an increase in speed
 acceleration does not just apply to speeding up. It can also
apply to **
It can also be a change in speed, a change in direction or a
change in both. So essentially- acceleration is a change in **
Example: in one second, we steadily increase our velocity form 30 km/h
to 35 km/h. In the next second, we go from 35 km/h to 40 km/h and so
on. So we are changing our velocity by 5 km/h each second. What is
our acceleration?
a = Δ v/ Δt
a = 5 km/h
1s
= 5 km/h/s or km/h s
or acceleration equals five kilometers per hour per second
Usually, scientists use m/s as velocity so acceleration would be m/s/s
or m/s2
Note: the unit for time is entered twice- once for velocity and once for
change in time.
Free fall- **
The amount of acceleration is the same **
Falling objects gains speed at a rate of 10 m/s each second.
a = change in speed = 10 m/s = 10 m/s2
time interval
1s
Acceleration due to free falling is 10 meters per second squared.
*****(It actually works out to 9.8 m/s2 which is the rate we use for
gravity on this planet)
Falling objects gain speed because of **
 If you throw an object straight upward it will move upward for
a while and then come back down. It loses 10 m/s for each
second going upward and gains 10 m/s for each second
moving downward.
3.2 Force Causes Acceleration
Any object that is accelerating is acted upon by a force- sometimes
more than one force.
 Acceleration depends on **. It is directly proportional to net
force
 Acceleration ~ Net Force

This means that **
The direction of acceleration is always **
3.3 Mass is the Measure of Inertia
The greater an object’s mass, the greater its **
That means it will require more force to accelerate something
heavier than something lighter.
If an object contains a lot of matter- heavy atoms or lots of lighter
atoms- it has a lot of mass.
Mass is not Volume
Volume is a **
meters, liters.
- it is measured in mL, cubic centimeters, cubic
Mass is the ** It is measured in g, kg, etc.
If an object has a large mass, it may or may not have a large
volume. An extra large bag of feather will have much less mass
than the same size bag of rocks!
Mass is Not Weight
Mass is the **
Weight depends on **. It is the force due to gravity acting on that
mass. If the gravity changes so does the weight.
But the mass **
Although mass and weight are different from each other, they are
directly proportional to each other. Objects with large mass have
large weight; objects with small mass have small weight.
Kilogram vs. Newton
SI unit for mass: **
SI unit for force: **
A one kilogram bag of something on this planet has a weight of
9.8N. Where the gravity is different, however, the weight will be
different
Kilogram vs pound: 1 kg weighs 2.2 lb.
3.4 Mass and Acceleration are Related
acceleration is inversely proportional to mass.
Acceleration ~ 1/mass
This means that when one gets larger, the other gets smaller
More mass means ** acceleration because there is more ** to
changes in motion.
3.5 Newton’s Second Law
**
equation: acceleration = net force/mass
acceleration is equal to the net force divided by the mass
a = F/m
a = acceleration F = net force
m = mass
Example: a 1000 kg car is being pulled by a cable with 2000 N of force.
What is the acceleration of the car?
a = 2000 N/ 1000 kg
Since 1 N = 1 kg *m/s2
a = 2000 kgm/s2 / 1000 kg = 2 m/s2
3.6 Friction
def- **
Friction is a force that arises when an objects rubs against something
else. Friction occurs for **
When a boat is propelled by its motor in one direction, water friction
impedes its progress.
When an object falls downward through the air, the force of friction
(called air drag) acts **
The amount of friction between two surfaces depends on **
Read about friction in your fingerprints on page 47. There will be
something on the test about this.
3.7 Objects in Free Fall accelerate at the same rate
Acceleration does not depend on mass for balls rolling down an
incline. They all have the same acceleration.
Acceleration of free fall doesn’t depend on mass. Objects**
The explanation comes from **
3.8 Why objects in free fall accelerate at the same rate
Newton’s second law tells us to consider not only the weight of the
object (its force) but also its mass.
All freely falling objects have the same force/mass ratio and undergo
the same acceleration
The acceleration due to gravity is represented by the symbol **
Consider a 10 kg boulder and a 1 kg stone
The weight of a 1 kg stone (or 1 kg of anything) is 10 N.
(conversion factor: 1 kg = 10 N)
Therefore the weight of a 10 kg boulder is 100N
Acceleration due to gravity is equal to an object’s weight divided by
its mass
a (g) = F / m
gravity (a) of stone = 10 N / 1 kg = 10 m/s2
gravity (a) of boulder = 100 N / 10 kg = 10 m/s2
They accelerate (fall) at the same rate even though there is a difference
in their size and mass
What about a feather and a coin
We know a feather will take longer to fall than a coin because **
BUT, if we put them both in a vacuum where air resistance isn’t a
factor, they will both fall at the same rate.
3.9 Air Drag
Read this section on your own and know the two factors that affect air
drag as well as the definitions for terminal speed and terminal
velocity
We will be discussing air drag later this year
Gliding pg 52
Read this page and be able to explain how gliding works and what
some of the special structures are that animals have evolved that
enable them to glide.