Transcript Newton`s Laws powerpoint

Amusement Park Forces
What is a Force?
FORCE = Any push or pull which causes
something to move or change its
speed or direction
Forces
Forces can be BALANCED or UNBALANCED
Not every force causes an object to move!

Balanced forces are equal in size and
opposite in direction

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.
Unbalanced forces
Can cause an object to start moving, stop
moving, or change direction.
Balanced forces have no
net force on them, and
therefore do not change
an object’s motion.
What is Gravity?
GRAVITY: An attraction force between
all masses in the universe
 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 of gravity it
exerts
The greater the distance, the less the force
Acceleration due to gravity = 9.8 m/s/s or 9.8 m/s2
This is how fast something accelerates as it is dropped (freefalling) towards Earth
Which has more of a gravitational pull on Earth, the sun or the
moon? The sun is larger, but the moon is closer!
Answer: The moon (remember the moon causes tides!)
Gravity in Space
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,
and the object stops accelerating and falls
at a constant speed
Terminal velocity is the highest velocity
that an object will reach as it falls
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 the
kinds of surfaces and the force pressing
the surfaces together

Changes motion into heat (rub your hands
together… the friction of your hands
rubbing together causes them to get warm)
What is Friction?
What are some ways athletes uses
friction?
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
 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
e) lawn bowling on a cut and rolled
lawn verses an uncut lawn
f) car turns left and you appear to
slide to the right
Examples of Newton’s 1st Law
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
e) Getting a friend to help you push a heavy box across the room
(increased force moves the box faster)
Examples of Newton’s 2nd Law
Examples of Newton’s 2nd Law
Definition: 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.
Huh?? 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.
Based on Newton’s 2nd law…
When driving, why is it more dangerous
to pull out in front of a truck
loaded with furniture, than it is to
pull out in front of an economy car?
Answer: the more heavy the vehicle, the harder it is to stop and the more
force it will hit you with.
Heavy trucks are hard to stop in time to avoid an accident, because it takes
more force to slow down a heavy truck than it does a light, economy car.
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
g) sprinklers rotating
Examples of Newton’s 3rd Law
What do these forces mean?
How must thrust relate to drag, in order for an airplane to move
forward?
How must lift relate to weight, in order for an airplane to lift off the
ground?
Work!
I.
You can make an object move if you
apply enough force on it.
II. When you lift a pencil, pull a sled,
or push a lawnmower, you are doing
work
III.Work is calculated by the formula:
W = f x d (Work = force x distance)
Work?
I.
If a student pushes very, very,
very hard against a wall with 200
Newtons of force, and becomes
exhausted and covered in sweat,
did he do any work?
II. W= f x d did the wall move? No!
Answer: W = 200 N x 0 m
III.W= 0 Nm (newton-meters)
IV. Was work done? No!
Calculate the work done:
I.
If a student pushes a 50N box (50
newtons, this is the weight of the
box) across the room 5.4 meters,
how much work was done?
II. W = f x d
III.W = 50N x 5.4 m
IV. W = 270 Nm