Download Newtons Laws - Cardinal Newman High School

Speed
Speed describes how fast something goes
 A cheetah moves faster than a horse, but how can we
determine this?


Speed= Distance Travelled
Time it took to travel
•
You will see this written as
•
Speed = d
t
Examples:
 A wheelchair racer finishes a 132 meter race in 18
seconds, what is his speed?


132meters
18 seconds
7.3 meters/sec

What is velocity and how is it different from speed?

Velocity: describes both speed AND direction
For example a lions speed maybe reported as 4.5 m/s
But in order to report its velocity we must know which direction it is
travelling



For example a possible velocity could be
4.5 m/s North, or 4.5 m/s towards the lake

Find the velocity in meters per second of a swimmer who
swims exactly 110 meters towards the shore in 72 seconds
110 m/ 72 s towards the shore

Calculate the distance in meters that a cyclist would travel
in 5 hours at a speed of 1200 meters per hour
S= d/t  1200 m/h = d/5hours
Solve for d:
D= 1200 m/h x 5 h = 6000 m
If a car and a train are driving along the same path at the
exact same speed, which will be harder to stop?
 Why? Train it has more momentum

Momentum: a quantity defined by both an objects velocity
and it’s mass
 Equation:


Momentum= mass x velocity

Calculate the momentum of a 6.00 kg bowling ball moving
at 10 m/s down the alley.

P= M x V
6.00 kg x 10 m/s
 =60 kgm/s


Acceleration: change in velocity divided by the time interval
in which the change occurs
a= final velocity – initial velocity
time

Practice Problems:
A flowerpot falls off a 2nd story windowsill. It starts from a rest and
hits the sidewalk 1.5 s later with a velocity of 14.7 m/s. Find the
average acceleration
2
(14.7m/s – 0m/s) / 1.5 s = m/s

John is riding his bike, and he accelerates from a speed of
2 m/s to 4 m/s in 3 seconds. What is his average
acceleration
(4 m/s– 2 m/s) / 1.5 s = m/s2

Lydia is driving on I-95, when she hits a traffic jam. She
slows down from a speed of 60 mph to a complete stop in
10 seconds. What is her average acceleration?
Have to convert 10 s  hours
10 s x (1 min/60 secs) x (1 hr/60 mins) =
.0027 hrs

Classwork(:0- 60 m/h)/.0027 hr = -22,000 m/h page 226
15 copy the question
Newtons Laws
Newtons 1st Law

“An object at rest remains at rest and an object in motion
remains in motion, unless it experiences an unbalanced
force”

Examples:
When you are in a car accident…


INERTIA: the tendancy of an object to remain at rest or in
motion with constant velocity

All object have inertia because they resist changes in motion
nd
Newtons 2

Law
The unbalanced force acting on an object always equals
the objects mass time its acceleration
F= ma
Force= mass x acceleration

Example: Pushing an empty shopping cart vs. pushing a
full shopping cart

If you push both carts with the same amount of force which will
go faster?
Newtons!

What does a “newton” represent?

Force is measured in “newtons”
1Newton (N)= 1 kg m/s2
1 Newton= .225 lbs


Example:

Zookeepers lift a stretcher holding a sick lion. The mass of
the lion and the stretcher is 175 kg. The acceleration
upwards is .657 m/s2. What force are the zookeepers using
to lift the lion?
175 kg x .657 m/s2=.

What is the necessary force for a 1600 kg car to accelerate
forward at 2m/s2
1600 kg x 2m/s2=

A baseball accelerates downward at 9.8 m/s2. If the force
acting on the baseball is 1.4 N, what is the baseballs
mass?
X kg x 9.8m/s2= 1.4 N 
1.4 N/9.8m/s2= Xkg
X=

A sailboat and its crew have a combined mass of 655 kg. If
it has a 895 N force acting on it, what is its acceleration?
655kg x Xm/s2= 895 N 
895 N/ 655kg = Xm/s2
X=
Free Fall

Free fall: the motion of a body/object when the only force
acting on it is gravity
r

The acceleration of gravity is always
9.8 m/s2

What’s the difference between mass and weight?
Weight
Weight= mass x gravity
-Weight is measured in newtons
Newtons 3rd Law

“For every action, there is an equal and opposite reaction”

For example: When you kick a soccer ball, do you feel
anything in your foot?


The force exerted on the ball by your foot is the action force,
while the force exerted on your foot by the ball is the reaction
force
CW page 240 #16