Download Newton`s First Law of Motion – The Law of Inertia

Chapter 2 Reading Guide:
Newton’s First Law of Motion – The Law of Inertia
Name:
Date:
Period:
Complete the Explore! Activity on page 17.
a.
Did the penny remain in place when you pulled the paper? YES
b. Did the speed with which you pulled make a difference? YES Explain: If I pulled slowly then the
coin came along with the paper. If I jerked the paper quickly the coin remained in place.
c.
Did the quarter work better than the penny? YES Why do you think this was so? The quarter was
bigger and had more mass so it resisted movement more than the penny.
2.2) Galileo’s Concept of Inertia (p.18)
1.
What did Galileo show about how lightweight and heavy objects fall?
Except for the effect of air resistance, objects of different weights fall to the ground at the same
rate.
2. What did Galileo reason about forces being needed to keep a moving object in motion?
He reasoned that no force was needed; that objectshave a tendancy to stay as they are, either
moving or stationary.
3. Define Inertia:
An object at rest tends to stay at rest, an object in motion tends to stay in motion.
4. Describe how Galileo used a rolling ball on a ramp to show the concept of Inertia.
If a ball rolled down a ramp does not lose its speed by rolling up another ramp, then it should not lose
its speed at all. (except of course for the effect of friction).
2.3) Galileo’s Concept of Speed and Velocity
1.
Define Speed in words:
Distance divided by Time
2. Write the equation for Speed:
Speed =
Distance
Time
3. Give three examples of speed units:
miles\hour
km/hour
meters/second (m/s)
4. What is the preferred unit of speed in science?
meters/second (m/s)
5. About how fast do you travel on the highway (65 mph) in meters/second?
17 – 20 m/s
6. How is Velocity different than Speed?
Velocity is speed in a given direction
7. What exactly does the term Constant Velocity mean?
Both constant speed and constant direction.
8. Write the question and answer for each Concept Check question on p. 22. ATTACH YOUR OWN PAPER.
Show your work completely. Attach your own work. Answers are with the questions in the book.
2.4) Motion is Relative (p 22)
9. Give an example of motion being relative: When you sit on a chair your speed is zero relative to the
earth, but is 30 km/s relative to the sun because the earth is in orbit around the sun at that speed.
2.5) NEWTON’S FIRST LAW OF MOTION – THE LAW OF INERTIA (p 22)
10. Write Newton’s First Law in the box below
Every object continues in a state of rest or uniform
(unchanged) motion unless acted on by a net force.
11. List at least two real examples of objects showing Inertia.
A hockey puck slides on the ice and loses very little speed. It tends to stay in motion.
The same hockey puck will not go far if slid across a cement parking lot because it is being acted on
by the unbalanced force of friction.
12. Write the question and answer to the Concept Check question on page 25. ATTACH YOUR OWN
PAPER. Attach your own work. Answers are with the questions in the book.
2.6) Net Force – The Combination of All Forces That Act on an Object.
13. Define Net Force:
The combination of all the forces acting on an object or system.
14. What is the scientific unit for Force Newtons (N)
15. Ask your teacher for a Spring Scale . Describe a one Newton force. Describe a 10-newton force.
(What could these forces accomplish?)
One Newton is barely enough to notice. It might be enough to move a pencil across a desk. A ten
newton force feels like about 2 pounds and is enough to slide a textbook across the desk.
See the figure at right:
a.
What does the length of each arrow represent?
The strength of the force
b. What does the direction of each arrow represent?
The direction of the force
c.
Describe how this figure illustrates the concept
of Net Force.
The net force is shown as the sum of all forces working in one direction, minus all the sum of all the
forces working in the opposite direction.
2.7) Equilibrium for Objects at Rest (p 26)
16. Define Equilibrium:
When the sum of all forces acting on an object is = zero.
17. What are the two forces acting on this bag of sugar (see diagram at right)?
Weight pulling downward and the Tension in the string supporting the bag pulling upward.
18. Draw arrows (vectors) on this diagram to show the forces and label the
arrows with the correct force names.
19. Which force is greater, tension in the spring or the weight of the sugar bag? (Trick question). They
are equal.
20. What does the  symbol stand for? The “Sum of”
21. State in words what this equation says:
The sum of all forces is equal to zero.
F = 0.
22. See the picture at right (Concept Check, p 28)
a.
If the gymnast hangs with her weight evenly divided between the
two ropes, how would the tension force in both supporting ropes
compare with her weight?
The tension force in each rope equals half her weight.
b. Suppose she hangs with slightly more of her weight supported by
the left ring. What would the tension in the right rope be?
The right rope tension would be less.
2.8) The Support Force – Why We Don’t Fall Through the Floor (p 28)
23. Define/describe the Support Force:
Aforce that works opposite gravity so we do not go falling the floor
24. What is another name for the support force?
The “Normal” force
25. Explain what this diagram (at right) is showing;
This diagram shows that the support force (or “normal”) is
always equal in size to the weight pushing doewn.
26. What is the Net Force on a bathroom scale when a 110 pound person stands on it? 110 pounds
27. Suppose you stand on two bathroom scales with your weight
evenly distributed between the two scales. What will each scale
read? Half your weight
28. How about if you lean and put more of your weight on one scale
than the other? That scale will read more than half your weight.
2.9) Equilibrium for moving objects (p 29)
29. Under what conditions is a moving object in equilibrium?
When it is moving a constant velocity a moving object is in equilibrium.
30. Why can a moving object not be in equilibrium if only one force is acting on it?
Because if only one force acts on an object then there can be no opposing force to balance it out.
31. If a box is pushed at constant velocity, how do we know the amount of friction acting on the box
compared to our pushing force?
The amount of friction is equal to the applied force if the box is moving at aconstant velocity.
32. Complete the Concept Check question on p. 30. Attach your own work. Answers are with the questions
in the book.