Newton

1
Newtons Laws Notes

• Continued You should have Newtons 3 Laws
  written already

Paco my goat!
2
A. Forces a push or a pull

• Frictional-
• Air Resistance-
• Gravity-
• Normal-

3
Drawing Free-Body Diagrams

• Free-body diagrams are diagrams used to show the
  relative magnitude and direction of all forces
  acting upon an object in a given situation. The
  size of the arrow in a free-body diagram is
  reflects the magnitude of the force. The
  direction of the arrow shows the direction which
  the force is acting.

• The free-body diagram to the right depicts four
  forces acting upon the object. Objects do not
  necessarily always have four forces acting upon
  them. There will be cases in which the number of
  forces depicted by a free-body diagram will

4

• A book is at rest on a table top. A free-body
  diagram for this situation looks like this

5

• A) A skydiver is descending with a constant
  velocity. Consider air resistance. B) Now Draw a
  skydiver with increasing velocity (still
  accelerating)

6
Equations

• Force mass x acceleration
• weight mass x gravity

7
Weight Calculations

• Jenny weighs 557 N on Earth. What is her mass in
  kg?

GIVEN F(W) 557 N m ? a(g) 10 m/s2
WORK W m g m W g m (557 N) (10
m/s2) m 55.7 kg
8
2. Soooooo. Which changes?

• Weight
• Mass

(CLICKER 2)
9
Lets watch a silly video on the difference
between mass and weight

• Raise your hand every time you hear information
  you have already learned!
• http//www.youtube.com/watch?vgrWG_U4sgS8
• Eureka- Episode 7 Weight vs. Mass

10
3. Soooooo. Which changes?

• Weight
• Mass
• 4. The gravity on Jupiter is 24.5 m/s/s. Do you
  weigh more or less there than on earth?

CLICKERS 3,4
11
Clicker 5

• Is the following statement true or false?
• An astronaut has less mass on the moon since the
  moon exerts a weaker gravitational force.

False! Mass does not depend on gravity, weight
does. The astronaut has less weight on the moon.
12
C. Air Resistance in Real Life

• Terminal Velocity
• maximum velocity reached by a falling object
• reached when Fgrav Fair

• no net force on object
• ? no acceleration
• ? constant velocity

13
What about the cat who fell 80 feet from a tree?

• http//www.youtube.com/watch?v_q_ULVhyfJg
• Cat falls from tree Youtube

14
What was the cats force as it fell?
F m x a

1. What was the cats force as it fell?
2. Weight?
3. What was the cats force on Jupiter? (g25.4
   m/s/s)

15
What now?

• Put CLICKERS AWAY
• Hand in Chapter 2 Reading Guide if you didnt
  yesterday
• Pick up Newtons Laws Worksheet
• (due Friday but try to get it done in class!)