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Thursday, 16 November 2006
Newtons Laws Test Prep
Now Playing: Newtons Laws Test Prep
Topic: Chap 6

Preparation for CP Newton’s Laws Test:

 

The test is mostly on Chapter 6, Newton’s Third Law but there are also some questions on Newton’s First Law (inertia) and Newton’s Second Law (F = ma)

 

Know that

  • Mass is in kg (kilograms)
  • Weight or force is in N (Newtons)
 

With Terminal Velocity

  • All forces are balanced
  • Net Force = zero
  • Acceleration = zero
  • Given the same parachute size, a heavy person reaches the ground first
 

Be able to calculate:

  • Convert mass to weight (mass * 9.8 = weight)
  • Convert weight to mass (weight / 9.8 = mass)
  • Calculate force, given mass and acceleration (F = ma)
  • Calculate acceleration, given force and mass (a = F/m)
  • Calculate mass, given force and acceleration (m = F/a)
 Some of the test is scantron:  bring a pencil

Posted by physicscp at 6:58 AM EST
Saturday, 4 November 2006
6.1 Forces and Interactions
Now Playing: 6.1 Forces and Interactions
Topic: Chap 6


CP Chap 6.1 to 6.4 Notes

 

6.1    Forces and Interactions

 

A force is not a thing in itself but it is part of an

 

INTERACTION

 

 

A mutual action between one thing and another

 

6.2    Newton’s Third Law

 

EVERY ACTION FORCE HAS AN EQUAL AND OPPOSITE REACTION FORCE

 

In every interaction,

  • Forces occur in pairs
  • The forces are between two objects

 

You must be able to exert an action force to get a reaction force back:

 

For example, walking on ice or jumping to shore from a boat below:

 

 

Question:

 

  1. Does a stick of dynamite contain force?

 

A car accelerates along a road.  Strictly speaking, what is the force that moves the car?


Posted by physicscp at 3:02 PM EST
6-3 Identifying Action and Reaction
Now Playing: 6-3 Identifying Action and Reaction
Topic: Chap 6


   

6-3 Identifying Action and Reaction

 

 

Action:  Object A exerts a force on object B

 

Reaction:  Object B exerts a force on object A

 

Question:  We know that the earth pulls on the moon. 

  • Does the moon also pull on the earth?

If so, which pull is stronger?


Posted by physicscp at 3:01 PM EST
6-4 Action and Reaction
Now Playing: 6-4 Action and Reaction
Topic: Chap 6
6-4  Action and Reaction on Different Masses 

The action/reaction forces are equal and opposite, but the effect of the force may not be equal:

 

 

 

Force of earth on boulder (the boulder’s weight)

Equals the force of boulder on earth

 

But because of the tremendous mass of the earth, the pull of the boulder on the earth is negligible!

 

 

 

Bullet:  F = a                Rifle:  F         =   a

             m                                                         m 

How Does a Rocket Work?  Does a Rocket require air to “push against?”

 

 

 

 

Question:  Can you identify the action and reaction forces of an object falling in the vacuum of outer space?

Posted by physicscp at 2:57 PM EST

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