Section 1.4

 define force  determine direction of acting forces and transfer of energy in examples  apply conditions of work to examples  calculate work and derive its unit from fundamental units  graphically determine work done on an object

 What is it?  If I place a ball on the desk and it is at rest, will it remain at rest? Why?  Force  Force : push or pull on an object ◦ In newtons (N)  What happens if I apply a force to the ball? Which direction is the force?  If there were no forces acting against my force, what would be the motion of the ball?

 For the following situations, make a sketch and label the forces present and their direction: ◦ Rolling a ball across a table ◦ Holding a ball in the air ◦ Bouncing a ball on the floor  What is happening to energy? How do you think it is related?

 What is work?  Work ◦ Done when a force moves an object through a distance in the direction of the force (so it is a vector quantity)  What are the units for work? How can we derive them? ◦ Joule (J) W = Fd

 A tugboat is towing a tanker through a canal using a towrope. Calculate work done by the tugboat if it applies an average horizontal force of 6.50 x 10 3 N on the towrope while towing the tanker through a horizontal distance of 150 m.  A large crane did 2.2 x 10 4 J of work in lifting a demolition ball a vertical distance of 9.5 m. Calculate the average force exerted by the chain of the crane on the demolition ball.

 What are the conditions, based on the definition? ◦ 1) must be movement ◦ 2) must be a force ◦ 3) force and distance object travels must be in the same direction  All three conditions must be met for work to be done

 Was work done? Which conditions are met/not met? ◦ Pushing a chair across the floor ◦ Person coasting on a bike ◦ Person carrying a backpack and walking forward ◦ Quarterback throwing a football

 A weightlifter lifts a 1000 N barbell a vertical distance of 2.30 m from the ground to a position above his head. He then holds the barbell above his head for a time period.  Is work being done the whole time? When does the weightlifter do work? What conditions are being met? If he isn’t doing work, what conditions are not being met?  What are the directions of the forces?

 As a group, analyze each other’s responses ◦ Were there any similarities? Differences? Why were their differences?  Come up with an answer as a group to the question  In 30 sec, tell the class what you think is happening

 Force applied to move an object a distance ◦ Work input ◦ W = Fd ◦ What happens on a force-distance graph if force is constant over a distance? What does area under the line represent? Work output= energy gained by the object

 If there are no outside forces, like friction, how will total work input be related to total work output?

 Energy = ability to do work  Describe how energy is transferred when: ◦ A pool cue hits a ball  What loses energy? What gains energy?  Change in energy = work  What will the units of energy be?