53 terms

# Conceptual Physics: Chapter 4- Newton's First Law of Motion - Inertia

#### Terms in this set (...)

Force cause ____
motion
Types of Motion:
1.____
2.____
1.natural motion
2. violent motion
Initially Natural Forces not thought of to be caused by forces. It only worked in what directions?
Straight up or straight down
Aristotle said that circular motion was natural for
and why?
the heavens
There is no end
Violent motion was
imposed motion
Violent motion was result of forces that
pushed or pulled
Violent motion moved objects that were in
their natural resting places
T or F: Old thinkers thought that Earth moved?
False. A force large enough to move Earth was unthinkable
Copernicus created the theory of
A moving Earth and other planets around the sun.
Galileo, a supporter of Copernicus, contributed to physics by demolishing that notion that ____ was necessary to keep an object moving
Force
Force is
any push or pull
Friction is
the name given to the force that acts between materials that touch as they move past each other.
Friction is caused by
irregularities in the surfaces of objects that are touching
Tendency of a moving body is
to keep moving.
Body to resist change is
inertia
Law of inertia
every object continues in a state of rest, or of motion in a straight line at a constant speed, unless it is compelled to change that state by forces exerted upon it
Why are forces needed in motion?
To overcome any friction that may be present and to set objects in motion initially.
In a force free environment, an object will
move in a straight line indefinitely
Amount of inertia in an object depends on
its mass
More mass is more or less inertia
more
T or F: How many kgs of matter an object contains and how much space the object occupies are the same thing
False
Mass overpowers what measurement in terms of inertia
Volume
Mass is
a measure of the amount of material in an object and depends only on the number of and kind of atoms that compose it.
Weight is
a measure of the gravitational force acting on the object
Weight depends on
an object's location
Objects with great mass have
great weight
1kg is equal to how many Newtons
9.8 N
Weight is equal to
mass * acceleration
In the absence of net force, objects
do not change their state of motion
Net force is
combination of all forces acting on an object
What changes an object's state of motion
Net Force
What is support force also called?
Normal Force
When an object is at rest, and the net force is zero, the object is in a state of
equilibrium
The resultant of forces must equal the object's ___ when the object is at equilibrium
Force (in Newtons)
Force is scalar or vector
vector
Tension is higher,
...
The vertical force of gravity affects
only the vertical motion
What distinction did Aristotle make between
natural motion and violent motion?
Natural motion is straight up or down, while violent motion is imposed.
Why was Copernicus reluctant to publish his ideas?
He feared persecution.
What is the effect of friction on a moving object?
It slows motion.
The speed of a ball increases as it rolls down an incline and decreases as it rolls up an incline. What happens to its speed on a smooth, horizontal surface?
No change (neglecting drag)
Galileo found that a ball rolling down one incline will pick up enough speed to roll up another. How high will it roll compared with its initial height?
To the same height if there is no friction
The law of inertia states that no force is required to maintain motion. Why, then, do you have to keep pedaling your bicycle to maintain motion?
To overcome friction
If you were in a spaceship and launched a cannonball into frictionless space, how much force would have to be exerted on the ball to keep it going?
None
Does a 2-kilogram rock have twice the mass of a 1-kilogram rock? Twice the inertia? Twice the weight (when weighed in the same loca- tion)?
Yes; yes; yes
Does a liter of molten lead have the same vol- ume as a liter of apple juice? Does it have the same mass?
Yes; no
Why do physicists say mass is more funda- mental than weight?
Mass is independent of location, while weight depends on the local gravity.
An elephant and a mouse would both have zero weight in gravity-free space. If they were moving toward you with the same speed, would they bump into you with the same effect? Explain.
The elephant has more inertia and is harder to stop.
What is the net force or, equivalently, the resultant force acting on an object in equilib- rium?
Zero
How does the tension in your arms compare when you let yourself dangle motionless by both arms and by one arm?
Double with one arm
A clothesline is under tension when you hang from it. Why is the tension greater when the clothesline is strung horizontally than when it hangs vertically?
The vertical components of the tension vector must add up to the weight, so the vectors along the rope will be very large.
If you hold a coin above your head while in a bus that is not moving, the coin will land at your feet when you drop it. Where will it land if the bus is moving in a straight line at con- stant speed? Explain.
At your feet because there is no horizontal acceleration
In the cabin of a jetliner that cruises at
600 km/h, a pillow drops from an overhead rack into your lap below. Since the jetliner is moving so fast, why doesn't the pillow slam into the rear of the compartment when it drops? What is the horizontal speed of the pillow relative to the ground? Relative to you inside the jetliner?
The pillow has the same horizontal speed as the plane; 600 km/h; zero.