How much work is done when a boy carries a 30N bag? Friday April 22nd, 2016 By the end of the day, you will be able to: Turn in Starters for the last unit On your new starter sheet, define the following terms in your own words. Work Power Get your lab notebook out of the crate. You will need it for class today. Explain how the scientific meaning of work and power differs from the everyday meaning. Experiment to determine how arm length affects the amount of work done And answer a question like this: How much work is done when a boy carries a 30N bag? Work Notes Work Lab & Practice

Work, Power, and Energy

Key Ideas/ Essential Questions How is work calculated? What is the relationship between work and power?

Everyday Meaning Which of the following is an example of work: bowling or reading? A man pushes against a brick wall, which doesn’t move. Is this an example of work? A student carries her books to class. Is this an example of work? A woman raises and lowers dumbbells at the gym. Is this an example of work? A book falls off a table and lands on the floor. Is this an example of work?

What is Work? work: the transfer of energy to an object by the application of a force that causes the object to move in the direction of the force Work is zero when an object is not moving. Work is measured in joules (J): 1 N • m = 1 J = 1 kg • m2/s2

KEY POINT Box moving = force being applied = work being done Work is ONLY being done while the FORCE is being applied, aka the object must ACCELERATE Not moving yet = no acceleration = no force = no work No longer moving= no work

What are the effects of work? #1 – object changes position (aka moves) #2 – object changes velocity (aka accelerates)

What is Work? How is work calculated? Work is calculated by multiplying the force by the distance over which the force is applied. work = force x distance, or W = Fd The force must be applied in the direction of the object’s motion. Force Distance moved

Example work Problem Imagine a father playing with his daughter by lifting her repeatedly in the air. How much work does he do with each lift if he lifts her 2.0 m and exerts an average force of 190 N? List the given and unknown values. Given : force, F= 190 N distance, d=2.0m Unknown: work, W= ? J Write the equation for work. Work = force x distance W= F x d Insert the known values into the equation and solve. W= 190N x 2.0m = 380 N*m W= 380 J

Independent Practice A luggage trolley is pushed 20 m up a slope with a force of 50 N in the same direction as the trolley moves. Calculate the work done. List the given and unknown values. Given : force, F= 50 N distance, d=20m Unkown: work, W= ? J Write the equation for work. Work = force x distance W= F x d Insert the known values into the equation and solve. W= 50N x 20m = 1000 N*m W= 1000 J

Work Mini-Lab Purpose: To determine how arm length affects the total work done when lifting an object repeatedly. Hypothesis: Pre-Lab Questions: What is the equation used to find the amount of work done? If you curl (exercise) an object, what distance would you use to find the work done? If you know the mass of an object, how can you determine what force will be needed in order to lift that object?

Measuring Your work Procedure Choose an item that your group will lift. (must be under 500g) Using the triple beam balance, find the mass of the object in grams. Then convert the mass into kg. Using the equation for weight, w=mg, calculate the force you will be using to lift the object. Measure and record the distance the object will be lifted. Calculate the work required for one lift. Count the number of lifts each person can make in 30 seconds. Calculate the total work done by each team member. Data Table Name Mass (kg) Force (N) Distance (m) Work of one lift (J) # of lifts in 30 seconds Total Work Done (J)

Exit Ticket How much work is required to pull a sled 5 meters if you use 60N of force? Tommy does 15 Joules of work to push the pencil over 1 meter. How much force did he use?  Angela uses a force of 25 Newtons to lift her grocery bag while doing 50 Joules of work. How far did she lift the grocery bags? The baseball player does 1234 Joules of work when hitting a baseball into left field. Assuming the baseball landed 100 meters away from home plate, how much force did the player use to hit the ball?

Exit Ticket A woman lifts her 100-newton child up 1 meter and carries her for a distance of 50 meters to her bedroom. How much work does the woman do? You pull your sled through the snow a distance of 500 meters with a force of 200 newtons. How much work did you do? An ant sits on the back of a mouse. The mouse carries the ant across the floor for a distance of 10 meters. Was there work done by the mouse? Explain. You did 170 joules of work lifting a 140 N backpack. How high did you lift the backpack? In problem 4, how much did the backpack weigh in pounds? (hint: there are 4.448 N in one pound?

A crane does 62,500 joules of work to lift a boulder a distance of 25 A crane does 62,500 joules of work to lift a boulder a distance of 25.0 meters. How much did the boulder weigh? (hint: the weight of an object is considered to be a force.) You lift a 45N bag of mulch 1.2 meters and carry it a distance of 10 meters to the garden. How much work was done? A 455N gymnast jumps upward a distance of 1.50 meters to reach the uneven parallel bars. How much work did she do before she even began her routine? It took a 500N ballerina a force of 250 joules to lift herself upward through the air. She landed a total of 2.5 meters to the left after completing her jump. How high did she jump? A people-moving conveyor-belt moves a 600 N person a distance of 100 meters through the airport. How much work was done?

What is the power of a motor that does 5000 J of work in 30 s? Monday April 25th, 2016 By the end of the day, you will be able to: Starter- What is the formula for work? The unit? Calculate the work done when a weight of 40N is raised by a height of 5.0m. A sled is pulled with 150 N of force. If the person pulling the sled does 405 J of work, what distance is the sled pulled? Explain how the scientific meaning of power differs from the everyday meaning and calculate power. Create an experiment to determine how much power is required to do pushups. And answer a question like this: Starter Review/Complete Work Lab Power Notes Power Mini-lab What is the power of a motor that does 5000 J of work in 30 s?

Power power: a quantity that measures the rate at which work is done or energy is transformed Power is measured in watts (W): 1 W = 1 J/s

How much time it takes to do a certain amount of work What is power? How much time it takes to do a certain amount of work

Both the rock climber and the hiker are going to the same place, so they are doing the same amount of WORK However, it will probably take the rock climber a lot longer to get there, meaning that her POWER is much lower

Power What is the relationship between work and power? Power is the rate at which work is done, or how much work is done in a given amount of time.

Example Power Problem Lifting an elevator 18 m takes 100000 J. If doing so takes 20 s, what is the average power of the elevator during the process? List the given and unknown values. Given : work, W= 100000 J time, t=20s distance, d= 18m Unkown: power, P= ? W Write the equation for power. Power= work / time P= W/t Insert the known values into the equation and solve. P= 100000J / 20s= 5000 J/s P= 5000 W

Independent Practice A motor does 5,000 joules of work in 20 seconds. What is the power of the motor? List the given and unknown values. Given : work, W= 5000 J time, t=20s Unkown: power, P= ? W Write the equation for work. Power= work / time P= W/t Insert the known values into the equation and solve. P= 5000 J / 20s= 250 J/s P= 250 W

Real World Application Work, Power, and Energy in Hockey http://www.nbclearn.com/portal/site/learn/science -of-nhl-hockey Work, Power, and Energy in Golf http://www.nbclearn.com/science-of-golf

Power Lab Question: Calculate the power of a person doing pushups. Materials: Meter stick, Stop watch, pencil, lab notebook Use the equations for work and power to guide your process. You must finish by the end of class. Don’t forget to include a hypothesis, procedure, data table, and conclusion!