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?