Title: Introduction to Newton
1Introduction to Newtons Laws
2Are heavier objects harder to stop when moving
than light objects? Why do you move to the
side of a car when the car turns a corner?
3Back in the day
Aristotle tried to answer the question of why
objects fall to Earth? By explaining that objects
would seek their natural position.
-This also explain why Earth didnt move. It was
already in its natural resting place at the
center of the universe.
-
This was, until Copernicus - came along and explained that the Earth orbited
the sun. - This was later backed up by Galileo and Newton
when they explained forces and motion in the
universe.
4Comparison between Aristotle and Galileo
- ARISTOTLE
- Things at rest were at their natural resting
place. - Objects that are moving away from their natural
resting place need to be continuously forced to
keep them moving
- Galileo
- Objects at rest stay at rest until something
forces them to do otherwise. - Objects in motion stay in motion unless something
forces it to do otherwise
5Newtons Laws
What are Newtons 3 Laws of motion?
- 1st Law An object at rest will stay at rest,
and an object in motion will stay in motion at
constant velocity, unless acted upon by an
unbalanced force. (Law of Inertia) - 2nd Law Force equals mass times acceleration.(F
ma) - 3rd Law For every action there is an equal and
opposite reaction. (All forces come in pairs)
6Newtons 1st LawLaw of Inertia
An object at rest will stay at rest, and an
object in motion will stay in motion at constant
velocity, unless acted upon by an unbalanced
force.
What does this all mean?
7What gives an object a lot of Inertia?
Volume the amount of space an object takes up
NO!!!!!!
8What gives an object a lot of Inertia?
Weight the effect that gravity has on an object
NO!!!!!!
9What gives an object a lot of Inertia?
Mass the amount of matter an object
possesses. -the amount of stuff something has
YES!!!!!!!!!!!!!!!!!
10Inertia
Inertia is an objects ability to resist a change
in motion.
- Derived from Latin meaning idleness or
laziness
Mass is directly related to Inertia. The more
mass you have, the more inertia you have.
11Newtonss 1st Law and You
Dont let this be you. Wear seat belts. Because
of inertia, objects (including you) resist
changes in their motion. When the car going 80
km/hour is stopped by the brick wall, your body
keeps moving at 80 km/hour.
12If Newtons 1st law is true
Why then, do we observe every day objects in
motion slowing down and becoming motionless
seemingly without an outside force?
13Friction!
- In the absence of a force of friction, an object
you - push would continue in motion with the same speed
- and direction - forever! (Or at least to the end
- of the table top.)
Friction is a type of force.
A force is a push or pull. -force is a vector
quantity (it has a size and direction)
14Up until this point, we have only been dealing
with objects at rest or moving with a constant
velocity.
Can we describe the motion of objects that dont
move at a constant velocity?
Yes!!! Things that arent moving at a constant
velocity are accelerating.
15Acceleration
Acceleration is how much velocity changes in a
certain amount of time.
Acceleration is a vector quantity.
The units for acceleration are meters per second
per second, or m/s2
16(No Transcript)
17Newtons 2nd Law
F ma
The net force of an object is equal to the
product of its mass and acceleration
18Newtons 2nd Law
If F ma then the units for force are kgm/s2
We call kgm/s2 Newtons (N)
19How much force is needed to accelerate a 1400
kilogram car 2 meters per second/per second?
Write the formula
Fill in given numbers and units
Solve for the unknown
20Another form of F ma
We can write this as What does this mean in
English?
21What is a net force?
The sum of all forces acting on an object in a
given direction.
1 N
3 N
2 N
22Free Body Diagrams
A free body diagram is a vector diagram that
shows how forces act on an object. - We
represent these forces with vectors (arrows) that
pull from the center of mass of the object.
10 N
5 N
If you push this box to the right with 5 N and
you push to the left with 10 N, what is the net
force on the object?
23Special types of Forces
Normal force is the force that is always
perpendicular to the surface of what ever an
object is sitting on. It generally opposes the
downward force of gravity.
When you sit in your chair, your body exerts a
downward force on the chair (your weight) and the
chair exerts an upward force on your body (known
as the Normal Force).
24Normal Force
Draw a Free Body Diagram of a 60 kg box sitting
on the floor.
F ma
FN 600 N
So m 60 kg a 10 m/s2
What is the net Force?
60 kg
F 60 kg x 10 m/s2 Fgravity 600 N
Fg 600 N
25Friction
- Friction is a force that opposes the motion of an
object. - In other words, friction will push in the
opposite direction of the way an object is
moving. - It slows down motion!
26Friction
Draw a free body diagram of a 30 kg box sitting
on a table. It is being pushed with a 20 N force
to the right, and there is a frictional force of
15 N.
FN 300 N
30 kg
Fp 20 N
Ff 15 N
Fg 300 N
What is the net force?