# Physics on Friday 9-28-07.

## Presentation on theme: "Physics on Friday 9-28-07."— Presentation transcript:

Physics on Friday

To do…Friday 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

To do Monday Hand in Handout #3 Hand in Graph work
Divide up, calculate velocity, calculate acceleration, determine overall velocity Forces- general information Forces –laws of motion Forces- free body diagram Homework #4 Test thursday

Any questions on the homework handout?
Results are due on Monday, if needed

New homework 3 more question on Handout #4
Grade old homework and pass back tomorrow Test on Friday (primarily constant acceleration problems and review)

Do Now 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 Vf = Vi + at 0 = a(1.5) = -3.6 m/s2

What causes objects to move or change their motion?

Forces Contact (applied) Forces Non-contact Forces
Electromagnetic forces (most common) Non-contact Forces Gravitational (most common) Fields Anything that pushes or pulls is a force Units in Newtons (for this class)

Weight is a Force Force due to the pull of gravity
Weight (W) = mass X acceleration due to gravity On earth, everything in free-fall accelerates at the same rate (9.8 m/s2) towards Earth

Demonstration that all objects are pulled at the same rate
Paper and book Paper-vs-paper The only reason why things do not fall at sam rate is air resistance

Take you weight in lbs and divide by 2.2 The 1st action converts from lbs  kg Kg is the common unit for Mass Mass is the amount of stuff that makes up an object

Mass is the measure of the inertia of an object
Inertia = the amount resistance to change in motion The object that is the most massive, changes its velocity the least when a constant force is applied Golf, Magic Tricks

Difference between mass and weight
Mass = measure of the amount of matter that makes up an object Weight is the amount of Force generated due to the pull of gravity

To find your weight in Newtons
Weight = mass x 9.8 9.8 = acceleration due to gravity on earth Change the location (moon, into space, on Jupiter): Change the acceleration value Moon 1/6th of earth = 1.67 Jupiter about 2.5 times Earth = 25

What weighs 1000 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

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