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

OROR YES NOYESNO

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 8 th 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 Time

To determine TIME: Time = Distance Speed 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 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 = F x D

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 ________Distanceor 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?