Transcript Work & Speed

Work &
Speed
YOURS:
TEXTBOOK:
Work is the transfer of energy
to an object by using a force
that causes the object to
move in the direction of the
force.
Work is done on an object if
two things happen: 1) the
object moves as a force is
applied, 2) the direction of the
object’s motion is the same
as the direction of the force.
Examples: pushing a ball up
a hill
YES OR NO
YES
OR
NO
YOURS:
TEXTBOOK:
A push or a pull
exerted on an object
in order to change
the motion of the
object; force has
size and direction.
Examples: people,
bulldozer, static
electricity
Work or Not Work?
Problem #1:
–Fabian carries a backpack from
the cafeteria to the 8th grade
hallway.
Problem #2:
–Alexis applies force to (pushes) a
cart.
Work or Not Work?
Problem #3:
–Kayla pushes a stack of books
across the floor.
Problem #4:
–Andrew wears a backpack and
climbs up the side of a mountain.
We have learned that
forces can change both
the direction and speed
of an object.
–For example…
To determine SPEED:
Average Speed = Distance
Time
To determine TIME:
Time =
Distance
Speed
To determine DISTANCE:
Distance = Speed x Time
Units of Measurement
Speed=miles per hour or meters per
second
Distance=meters, miles, kilometers…
Force=newtons
Work=joules or newton-meters
How long does it take to travel:
a. 120 miles at 40 mph
b. 60 miles at 40 mph
c. 390 miles at 60 mph
Calculate the distance that you would travel
if you drove for:
1. 3 hours at 20 mph
2. 10 hours at 60 mph
3. 5 hours at 45 mph
Practice Problem #1:
--Daniela drives a car 100 miles (m)
in 2 hours (h). Using the formula for
speed, determine Daniela’s
average speed during that time.
Practice Problem #2:
--Klelian jogs to her house 72 meters
(m) away in a time of 36 seconds
(s). What is Klelian’s average
speed?
Practice Problem #3:
--If you travel 7 kilometers (km) and
walk for 1 hour (h), what is your
average speed?
Practice Problem #4:
--An airplane traveling from Atlanta to
Las Vegas travels 1,260 km in 3 h.
What is the airplane’s average
speed?
Practice Problem #5:
Tammie cycles 20 miles per hour on
her bike for 4 hours. How far does
Tammie cycle in this time?
Final Practice Problem….
If you rode your bike 2 hours and
traveled 24 miles, what is your rate
of speed?
Example #1:
--On vacation to Florida, Alexia’s
family traveled 300 miles at 30
mph. How long did the trip take?
Example #2:
--Cristian drove his truck from
Nashville to Chicago at a rate of 30
miles per hour. How far could
Cristian drive in 3 hours?
Example #3:
--Daniel drove his red Dodge Charger
at an average speed of 100
kilometers per hour for 10 hours on
a country road. How far did Daniel
travel?
Test Bonus Question:
A snail moves at a distance of 8
meters in 2 hours. Calculate the
average speed of the snail.
To leave class…
Which of these statements is true about
a moving object that increases its
speed?
A. The object’s mass increased.
B. The object is not accelerating.
C. A force is acting on the object.
D. No forces are acting on the object.
The equation for WORK is…
Work = Force x Distance
or
W=FxD
Work Problem #1:
--Kammi uses a lever to lift a large
stone from the ground. Kammi
applies a force of 50 newtons and
moves the stone 5 meters. How
much work is being done by
Kammi?
Work Problem #2:
--Mariah wants to move a stack of
magazines from one room of her
house to another. Using a wheel
and axle, Mariah applies a force of
100 newtons and moves the stack
10 meters. How much work is being
done by Mariah?
The equation for FORCE is…
Force =
Work
________
Distance
or
F= W
______
D
Force problem #1:
--Ashley performed 100 joules of
work by moving a pile of rocks 10
meters with a lever. What was the
force on the rocks?
Force Problem #2:
-Cameron performed 500 joules of
work by lifting a car 50 meters with
a pulley. What was the force on the
car?
VELOCITY
The measure of an object’s
SPEED and DIRECTION
Example: 1. a person walks 5 m/h east
2. a bird flies 10 km/h north
Think…
Imagine that two birds leave the
same tree at the same time.
They both fly at 10 km/h for 5
min, 12 km/h for 8 min, and 5
km/h for 10 min. Why don’t they
end up at the same place?
Velocity changes if:
1. Speed changes
OR
2. Direction changes
For example: a bus traveling at 15
m/s south speeds up to 20 m/s
south
Acceleration
The rate at which velocity
changes (either speed or
direction)
Which of the following is NOT
an example of acceleration?
A. a person jogging at 3 m/s along a
winding path
B. a car stopping at a stop sign
C. a cheetah running 27 m/s east
D. a plane taking off
Problem Examples:
1. Create 5 VELOCITY examples
*****For example: a person travels 5 mph
north)
2. Create 5 speed word problems
*****For example: A student travels 10
miles for 1 hour. What is their
average speed?