1. Phys 1-28 Monday Homework Work

2. Final Homework on Conservation of momentum Pages 870-871 Questions 8-12

3. To do Work on an object… Apply a force to the object, which results in the object’s displacement Only the part of the applied force in the object’s direction of the motion does the work

4. Equation W = F d (if in one dimension) W = work done F = force applied d = displacement of object W = f cosθ d (if only a part of force is doing work) Θ = angle between directions of force and motion

5. Units Joules (J) Named after James Prescott Joules For his work in relating heat, work and energy

6. How much work is equal to 1 Joule 1 J = 1N times 1 m The force of gravity on a small apple is equal to 1 Newton The work done by gravity as an apple drops 1 meter = 1J

7. How much work is done on you when you climb stairs?

8. How much work is done on you as you climb the stairs? Discount the force moving you horizontally (hard to quantify) What force pushes you upward? How could you find a number value for that force? What is the value for you?

9. So… For someone walking at a constant rate: The downward force of your weight is equal to the normal force of the ground

10. To find the amount of work done Find the vertical displacement of the trip (in meters) Multiply by the normal force of the stairs Answer is in Newtons Compare with others in class

11. Is the amount of work done on an object dependent on time?

12. NO Only force and displacement If the product of the force and displacement is the same on 2 objects, the same amount of work has been done to each

13. Power Is a measure of the rate at which work is done to an object A ratio of work to time P = W / t

14. Units for power is Watts (W) James Watts Created a more efficient steam engines Scottish inventor and mechanical engineer

15. Light Bulbs The number associated with a light bulb indicates work is done to make light per second More work is done in a 60 W bulb versus a 20 W bulb every second

16. Gathering data You will be assigned a stairwell Each group is to find the vertical height of the stairwell Each student is asked to find the time it takes them walk from the bottom to the top of a stairwell at a constant rate.

17. The data you should have gathered: Weight of yourself: _________ Height of stairwell (in Meters): _______ Time it takes you to climb the stairs: _____ in seconds