    Take out your lab paper from last week. You may discuss with a partner but you must write down your own responses How did you find the acceleration of the cart in this lab?

The acceleration of the cart was the same as what other object in the lab?

How did you calculate Fnet? Which mass did you use to find Fnet? Why?

 Reminder: Newton’s Second Law Labs will be due Tuesday October 26. Please come in for coach class if you need help!!!

1.

2.

What does the word “force” make you think of?

What are some ways you have used the word “force” in your life?

 An object at rest will stay at rest or in constant straight line motion (a=0) force UNLESS acted on by a nonzero net

 An object is accelerating if it is EITHER changing speed and/or changing direction (ex. A car making a right turn but keeping the same speed)

 the tendency of an object to resist a change in motion. This is quantified by its mass .



Imagine you are standing in a stationary bus. Suddenly the bus starts moving. What happens?



You fall backwards!

This is due to the inertia of your body. When the bus was at rest, you were also at rest. When the bus started moving, your legs went with the floor of the bus due to friction. But the upper part of your body tends to continue in its state of rest (inertia of rest). As a result you fall backwards.

  Braking in a car: down. Hopefully you'd be wearing your seat belt because that would be the outside force. The seat belt stops you from flying through the windshield. If not, then the windshield is the outside force slowing you Turning in a car: That is inertia because your body wants to go straight but the outside force (aka the car) is turning you.

  An object which is accelerating has a nonzero net force acting on it equal to the object’s mass times its acceleration.

i.e.

F = ma

 The same force exerted on a larger mass produces a smaller acceleration.

   Force is measured in Newtons represented by a capital N , 1 N = 1 kg x m/s 2 One Newton 7 Fig Newtons is approximately

  a=5 m/s 2 , m = 4 kg F = ?

F = ma = (5 m/s 2 )(4 kg) = 20 N

A golfer applies a force of 6 N to a 0.5 kg golf ball. What is the ball’s acceleration?

F = ma  a = F/m a =F/m=(6 N)/(0.5 kg)=12 m/s 2



Use the rest of class to work on the worksheet “Newton’s Laws.” It will be due on Monday 11/21/11

  Read the article: “As Injuries Rise, Scant Oversight of Helmet Safety” on www.nytimes.com

(you may have to search for it) Write as detailed a description of the article as possible explaining how concepts we have talked about in physics class appear in this investigation. The longer and better the description, the more points!!!

1.

2.

A baseball pitcher throws a ball by applying a force of 25 N to it. The ball accelerates at 50 m/s 2 . What is the ball’s mass?

You are standing on a moving bus when it suddenly brakes. Describe what happens and why.

    A force is any influence that causes an object to accelerate (usually a push or pull) Forces are vector quantities Represented by a force vector Every force vector should have an arrowhead, a tail, and a label

  Symbol: F f Definition: The contact force that opposes sliding motion between surfaces

F f

  Symbol: F N Definition: the contact force exerted by a surface on an object; acts perpendicular to the surface

F N

  Symbol: F T Definition: the pull exerted by a string, rope, or cable when attached to a body and pulled taut

F T

  Symbol: F thrust Definition: a general term for the forces that move objects such as rockets, planes, cars and people

  Symbol: F g Definition: a long-range force due to gravitational attraction between two objects, generally earth and an object

F g

 Forces come from the CENTER of the object!

 Work with your groups to complete STEP 1 on your paper (add the correct forces to your selected diagram). You may draw them right onto the paper.

  BALANCED FORCES: If net force is 0, there is no acceleration (v is either 0 or constant) UNBALANCED FORCES: If net force is nonzero, there is acceleration.

 Work with your groups to complete STEP 2 on your paper (determine whether the forces are balanced or unbalanced). When you finish, tape your paper to the blackboard in the back.

 Use the rest of class to work on the paper “Balanced and Unbalanced Forces.” It will be due at the end of class.

  Use the rest of class to fill in your chart. You may use classroom textbooks (p. 123) to help you.

After you have finished your chart, you may continue working on your homework (Newton’s Laws Worksheet)

 Fill in the force vectors in the following diagrams. Be sure to include ALL forces!!! 1.

A car traveling at 60 mph 2.

(a ball rolling down a hill)

  Weight is the force of gravity (represented by F g) F g =mg

where m=mass and g=acceleration due to gravity (on earth: -9.8 m/s

2

)

    Step 1: Write down your weight in pounds. If you don’t know your weight or don’t want to write it, make something up. Step 2: To convert your weight into Newtons, multiply your weight in pounds by 4.448221 or 4.45

Step 3: Write that weight in the weight column next to “Earth” Step 4: Follow the directions on the rest of the worksheet. Happy Friday 