Announcements Warm up… Convert 1) 50.9 kg= ___ g 2) 107 Gs= ___ s Agenda for the day: Notes-Work Vocab quiz-Friday

Re-teach ☺ A cross country runner travels 1 km in the first 5 minutes, 1 km in the second 5 minutes and 1 km in the third 5 minutes…her acceleration is__________.

Fill in the blank with the same word I ____ ON SCIENCE PROBLEMS MY PARENTS ____ FOR A LIVING AFTER I DROPPED IT, MY PHONE DOESN’T ____ CLEANING MY ROOM IS TOO MUCH ____

Educational Objectives CONTENT-SWBAT DEFINE AND DESCRIBE WORK LANGUAGE-SW CALCULATE THE WORK DONE IN JOULES FOR SITUATIONS INVOLVING FORCE AND DISTANCE

Work Formula: Work done = force x distance . Definition- “Transfer of energy”..It is the energy used to move something over a distance; it is done by Forces ON AN OBJECT or..”it is done by something on something else” Formula: Work done = force x distance W=F∥ x d (what type of relationship, direct or indirect?) Unit: N-m : Joule

Picture for your energy book

Looking ahead-Work 1) Simplest-when force /displacement in same direction 2) force and displacement different directions 3) when work done on an object is acted on by more than 1 force

Work = Force x distance Remember- It is a measurable change and it is caused by a force

Work …the motion has to take place (parallel) in the direction of the force

Work or no work? A girl pulls her dog, but the dog won’t budge A book falls off a table and free falls to the ground. A rocket accelerates through space.

Work …the motion (distance) is parallel to the direction of the force 1) When does the waiter do work? When he picks up the tray 2) When does the waiter not do work? When he carries the tray

I Who is doing work? Why?

Practice One species of Darwin’s finch can exert a force of 205 N with its beak as it cracks open a seed. It its beak moves through a distance of 0.40 cm, how much work does the finch do to get the seed? W=Fxd = 205 N (0.0040 m) = 0.82 J

How much work does the intern do by pushing for a distance of 2.5 m? An intern pushes a 72 kg patient on a 15 kg gurney, producing an acceleration of 0.60 m/s² How much work does the intern do by pushing for a distance of 2.5 m? How far must the intern push the gurney to do 140 J of work?

Announcements Warm up… Convert 1) 42.2 µg= ___ g 2) 65.4 N= ___ nN Agenda for the day: Notes-Work Vocab quiz-Friday

Review Work is done _____ an object when you transfer ______ to that object. Formula? 2 different units? Determine whether work was done on not done: An ice skater glides for 2 meters across the ice The ice skater’s partner lifts her up a distance of 1 m An ice skater’s partner carries her across the ice a distance of 3 meters After setting her down, the ice skater pulls her across the ice a distance of 10 m After practice, the skater lifts her 20N gym back up 0.5 m

2nd definition of Work When a force is exerted on an object at an angle to the horizontal, only a part of the force causes a horizontal displacement

Picture for Energy book W= (F•cosθ)d Θ is the angle between the force and the displacement of the object The y component does not contribute to work done on the object

Practice Problem d

Work always requires a system of more than just one object Remember Work always requires a system of more than just one object A nail cannot do work on itself, but a hammer can do work on the nail by driving it into wood

Avoid using “any ‘ole angle” The force is always applied parallel to the incline. The displacement of the cart is also parallel to the incline. Since F and d are in the same direction, the angle theta in the work equation is 0 degrees. Most students experience the strong temptation to measure the angle of incline Don't forget: the angle in the equation is not just any 'ole angle. It is defined as the angle between the force and the displacement vector..

Review Can the normal force do work on an object? Why or why not? A crate with a weight of 1300 N (mg) rests on the floor. How much work is required to push it at a constant speed 4 m against a friction force of 230 N? How much work to lift it vertically 4 m?

Do the following problems in your Energy book P 220 # 67, 68 and 70

Negative Work?! A force acting upon a moving object can hinder a displacement. The force acts in the direction opposite the objects motion in order to slow it down. The force doesn't cause the displacement but rather hinders it.

Work against gravity only depends on height Because gravity only pulls down..it does not matter which path you take The amount of work is the same, but you apply the force over a longer distance