Transcript Physics on Friday - elyceum

Physics on Friday
9-28-07
To do…
• Answers for first test
• Questions on Homework handout
• Class example problem
• Hand in the graph created by you walking before
the motion detector with the analysis
• Talk about the causes of motion
Any questions on the
homework handout?
Results are due Monday,
if needed
New problem
• Joe runs with a constant velocity of
5.4 m/s for 20 s before he reaches a pile of
leaves. It takes 1.5 s for Joe to come to a stop
in the pile. What is his rate of acceleration in
the leaf pile and how far did Joe travel overall?
Answer
What causes objects to move
or change their motion?
Forces !
• A force is anything that creates a push or
pull on an object
• Forces from contact
• Forces at a distance
• Units (Newtons-vs-Pounds)
What weighs 1000 N?
Determine your weight in Newtons
• Take you weight in lbs and divide by 2.2
• Then multiply the result by 9.8.
• The 1st action converts from lbs  kg
• The 2nd action converts from kg  N
Football player (220 lbs)
What weighs 100 N?
Freshman backpacks
What weighs 10 N?
The average textbook
What weighs 1 N?
A smallish apple
Homework in book
• What force is necessary to accelerate a
1250 kg car at a rate of 40 m/s2?