Monday, January 30, 2017

Activity 79: Introduction to Torque


Activity 75.10


Read Chapter Sections 9.1, 9.2, and 9.3 in the textbook.

Activity 75.20 -

Watch this video on torque


  • Torque is the result of applying a force on an object somewhere other than it's center of gravity.
  • Torque causes an object to rotate.
  • At its most basic level Torque is calculated by multiplying the Force applied times the Distance the force is from the object's pivot point.
  • Torque = Force X Distance.
  • Torque = (Force) (sin(angle)) (Distance)
  • The angle referenced above is the angle between the applied force and the axis of the rotation of the object.  



Example

In the picture above the two people are sitting on a see saw.  
Question:  How far from the center does the person on the right need to sit to balance the see saw?

The person on the left is generating a force of (30 kg X 9.8 m/s/s) = 294 N .  This force is creating a torque of (294N ) (2.0m) = 588Nm of counter clockwise torque of the left side of the see saw.

To put the see saw in balance (called rotational equilibrium) the counterclockwise torque must equal the clockwise torque.   This is often written Tc = Tcc.  

In this case the person sitting on the right side must generate 588Nm of clockwise torque to put the see saw in rotational equilibrium.  Since they weigh (50kg x 9.8m/s/s) or 490N they must sit (588Nm/490N) or  1.2m from the center.



Activity 79.10

Complete this Introduction to Torque Google Classroom activity collecting the data fro the class demonstration.


Activity 79.22

Pick up a paper copy of these seminar problems.  Look at the first problem and come up with an approach to solve it.  Check your answer against the solution in the answer key.  When you are done with the rest of the problems please check your answers here.


Activity 79.25

Pick up a paper copy of this document on concurrent forces.  Make sure you understand the difference between concurrent and nonconcurrent forces.


Activity 79.30


Pick up a paper copy of torque problem set #1.  When you are done check your answers here.


Activity 79.40

Pick up a paper copy of torque problem set #2.   When you are done check your answers here.




Thursday, January 26, 2017

Activity 77:Banked Track & Newtons' Universal Law of Gravitation












            



Newton's Universal Law of Gravity


Calculate g


Constants for Homework
Mass of the Moon: 7.35E22 kg
Distance from the Earth to the Moon: 3.84E8 m
Radius of the Moon: 1.74E6m

Homework Problems   23, 24, 29, 31, 33, 34, 35






Tuesday, January 24, 2017

Activity 76: Centripetal Acceleration and Centripetal Force



Read Section 6.2 in the textbook






Equations from yesterday

radians = arc length/radius

angular velocity  = radians/second

velocity =  radius X angular velocity


Acceleration = change in velocity/time





Substituting v = rω into the above expression, we find ac = (rω)2 / r = rω^2.


So centripetal acceleration equals the following:

 Centripetal Acceleration

From Newton's 2nd law we know:
and substituting in acceleration from the above equation gives:



So why does the water stay in the pail?


Complete Questions 10, 11, 13, 14  and the end of chapter 6:

 when done Check your answers here....



Activity 75: Introduction to Circular Motion





Read the notes below on the definition of a radian, and the definition of angular velocity.  We can think of an angular change in circular motion in either degrees or radians.  They can be converted from one to another with the conversion formula 2(Pi)r = 360 degrees.


As we move through our study of circular motion you should quickly see the benefit of viewing angular changes in radians rather than degrees.

Remember when using your calculator with radians to set the mode from degrees to radians in your calculator.

Take a look at problems 1,2,3,4, 5, 6 &7 at the end of the section.  Check your answers here....



Circular Motion Unit Learning Objectives



Rotation Angle and Angular Velocity

Greek Alphabet




Angle Measurement in Radians not Degrees



s = ARC LENGTH

r = radius


Radian = s/r

























Linear Velocity 

Since 
                           Δs = rΔθ 


Linear Velocity = radius times angular velocity










Thursday, January 5, 2017

Activity 74: Momentum Seminar Problems 5-8 & Momentum Problem Set #2


Activity 73.10


Read Section 8.3 in the textbook.  The basic concept here is straightforward.

  • The total Momentum (summation of all mv's) in a closed system never changes
  • Momentum is a vector,  the direction of the velocity matters.  If you have a head on collision between two moving objects then before the collision one object will have a positive velocity and the other a negative velocity so the total momentum before the collision must equal                    ( m1v1) + ( m2(-v2))
  • That total momentum will equal the momentum of the system after the collision.



Pick up a paper copy of these Momentum Seminar Problems 5-8.   As you work through them you can watch this video for an explanation on how to solve them.






The answer key can be found here.

Activity 69.20

Pick up a paper copy of momentum problem set #2.  When done review your answers here.




Activity 73: Momentum PS#1

Activity 68.10

Pick up a paper copy of this worksheet.  When you are done check your answers here.

Activity 72: Introduction to Impulse and Momentum


Activity 72.10 Introduction to Momentum

Watch this introductory video to impulse & momentum










Pick up copies of the Momentum Seminar Problems 1-4.   My suggestion is that you try these problems in sequence and then watch this video which goes over the solutions to these problems.






Tuesday, January 3, 2017

Activity 70: Introduction to Circular Motion





Read the notes below on the definition of a radian, and the definition of angular velocity.  We can think of an angular change in circular motion in either degrees or radians.  They can be converted from one to another with the conversion formula 2(Pi)r = 360 degrees.


As we move through our study of circular motion you should quickly see the benefit of viewing angular changes in radians rather than degrees.

Remember when using your calculator with radians to set the mode from degrees to radians in your calculator.

Take a look at problems 1,2,3,4, & 5  at the end of the section.  Check your answers here....



Circular Motion Unit Learning Objectives



Rotation Angle and Angular Velocity

Greek Alphabet




Angle Measurement in Radians not Degrees



s = ARC LENGTH

r = radius


Radian = s/r

























Linear Velocity 

Since 
                           Δs = rΔθ 


Linear Velocity = radius times angular velocity