Transcript Newton`s Laws First Law --an object at rest tends to stay at rest AND

Forces
* Newton’s Laws
And
Speed
Newton’s Laws
First Law An object at rest tends to stay
at rest AND an object in
motion tends to stay in
motion.
Second Law The acceleration of an object depends on the
net force acting on the object and the
object’s mass
<Force needed to change object’s speed
depends on MASS & ACCELERATION>
Third law When one object exerts a force on a second
object, the second object exerts an equal
and opposite force on the first.
<for every action, there is an ___ & ____
reaction!>
Motion (or lack of motion) cannot change
without an unbalanced force acting.
Balanced forces
Tug of war - teams pull in opposite
directions
If teams pull with the same force, in
opposite directions, net force on the
rope is ZERO and
---> Rope doesn’t move
Unbalanced forces
• To move the rope, one team must pull
harder than the other.
Net force is NOT zero
Rope will MOVE
* Only unbalanced forces cause an object
to MOVE (speed up, slow down or
change direction).
Average speed is described as a measure of
distance divided by time.
*Time can be in seconds, minutes, hours
*Distance can be meters, kilometers
*Speed is a combination of the two: m/s,
km/hr
Speed = distance
time
or v = d/t
Distance = speed X time
or
Time = distance
speed
t = d/v
or
d = vt
Velocity and speed are very
similar ideas.
Velocity is the rate of motion (the speed) in a specific
DIRECTION.
Example: I'm going that-a-way at 30 kilometers per
hour.
--> My velocity is 30 kilometers per hour that-away.
For velocity you must have both values ->
speed and direction.
Direction can be described in many ways:
*east, west, south, north
When velocity is changing, the word
acceleration is used.
*You speed up if the acceleration and
velocity point in the same direction.
* You slow down (decelerating) if the
acceleration and velocity point in
opposite directions.
Momentum is in the same direction as velocity.
--> indication of how hard it would be to stop an
object.
Example --> If you have a tennis ball and a bowling ball
both traveling at 3 meters per second, which
has greater momentum?
Which would be HARDER to STOP?
*Right! The bowling ball has a greater momentum, it
has more mass.
To calculate momentum:
Momentum = mass X velocity
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A runner finishes a 135 meter race in 24 seconds.
What is the runner’s average speed?
Find the velocity in meters of a swimmer who swims
exactly 110 m toward the shore in 72 s.
Find the velocity in meters per second of a baseball
thrown 38 m from third base to first base in 1.7 s.
Calculate the momentum of a 8 kg bowling ball
moving at 12.0 m/s down the alley.
An athlete with a mass of 73 kg runs with a constant
forward velocity of 1.50m/s. What is their momentum?