Class Notes 28 September Turn in HW / Pick up HW Today: Drawing a picture is required Units are required on all numbers Directions of a & F answers? ALL: Start from SF=ma, SF=0 #3: mass 55 kg #2,3: Directions on F and a! #4: Sorry for duplicate on HW16 Today: Tension, Friction

Which of Newton’s law does the bow and arrow display? 3rd 1&2 1&3 2&3 All 2016 Votes: 0, 0, 0, 1, 2, 3, 8

Putting it all together FREE BODY DIAGRAMS! A diagram separating the ONE object of interest and showing ALL the forces acting on it. Some things to remember Strings can only pull Pulleys have no friction Draw FBDs, coordinate system Write equations (SF=ma) (x & y) Solve! Handout Sheet

Example A force pulls on a 4.00-kg block at an angle of 30.0°, with a force of 20.0 N. What is the normal force? What is the acceleration? What is its velocity and how far has it traveled after 5.00 s? 29.2 N , 4.33 m/s2 29.2 N , 4.33 m/s2, 21.7 m/s,54.1 m

Various Demonstrations Various tension questions and demos with scales and strings. 1 scale, 1 500-g mass  1 scale, 2 500-g masses  2 scales, 500-g mass on one side held on the other  2 scales, 2 masses, one on each end  FT=5N

What will the scale read? 0 N 2.5 N 5.0 N 7.5 N 10. N Somthing else 2016 Votes: 5, 0 ,4, 1, 3, 0 Now I put it over a pulley

Various Demonstrations Various tension questions and demos with scales and strings. 1 scale, 1 500-g mass  1 scale, 2 500-g masses  2 scales, 500-g mass on one side held on the other  2 scales, 2 masses, one on each end  FT=5N FT=5N

What will each scale read? 0 N, 5.0 N 2.5 N, 2.5 N 5.0 N, 5.0 N 5.0 N, 0 N 10. N, 10.0 N Something else 2016 Votes: 1, 3, 8, 0, 0, 0

Various Demonstrations Various tension questions and demos with scales and strings. 1 scale, 1 500-g mass  1 scale, 2 500-g masses  2 scales, 500-g mass on one side held on the other  2 scales, 2 masses, one on each end  FT=5N FT=5N FT=5N on each

What will each scale read? 0 N, 5.0 N 2.5 N, 2.5 N 5.0 N, 5.0 N 5.0 N, 0 N 10. N, 10. N Something else 2016 Votes: 0, 0, 10, 0, 3, 0

Various Demonstrations Various tension questions and demos with scales and strings. 1 scale, 1 500-g mass  1 scale, 2 500-g masses  2 scales, 500-g mass on one side held on the other  2 scales, 2 masses, one on each end  FT=5N FT=5N FT=5N on each Each reads FT=5N

Homework Read Chapter 4.8 – 4.9 Do problems on Worksheet HW#17: WebAssign You will turn in all your FBDs A FBD must be included for EVERY PROBLEM in chapters 4 and 5