# Physics: Chapter 2

Flashcard maker : Lily Taylor
inertia
the property of things to resist changes in motion
newton’s first law of motion ( the law of inertia)
every object continues in a state of rest of uniform speed in a straight line unless acted on by a nonzero net force
force
in the simplest sense, a push or a pull
net force
the vector drawn to scale used to represent a vector quantity
vector
an arrow drawn to scale used to represent a vector quantity
vector quantity
a quantity that has both magnitude and direction, such as force
scala quantity
a quantity that has magnitude but not direction, such as mass and volume
resultant
the net result of a combination of two or more vectors
mechanical equilibrium
the state of an object or system of objects for which there are no changes in motion. In accord with Newton’s first law, if an object is at rest, the state of rest persists. If an object is moving, its motion continues without change
equilibrium rule
for any object or system of objects in equilibrium, the sum of the forces acting equals zero.
What relationship between the Sun and Earth did Copernicus formulate?
The Earth revolved in a circle about the Sun.
What two classes of motion did Aristotle advocate?
Natural motion and violent motion
What did Galileo discover in his legendary experiment on the Leaning Tower of Pisa?
Galileo found that a heavier stone does not fall significantly faster than a lighter one.
What did Galileo discover about moving bodies and force in his experiments with inclined planes?
In the absence of a retarding force, a body will keep moving at a constant speed in a straight line forever.
What did Copernicus say about the motion of the Sun?
The Sun is stationary and Earth circles it.
How does Newton’s first law of motion relate to Galileo’s concept of inertia?
Newton refined Galileo’s concept of inertia and made it his first law of motion.
What type of path does a moving object follow in the absence of a force?
It continues to move in a straight line at a constant speed.
What is the net force on a cart that is pulled to the right with 100 pounds of force and to the left with 30 pounds of force?
The net force is 70 pounds to the right.
Why do we say that force is a vector quantity?
A force has a magnitude and a direction.
According to the parallelogram rule, what quantity is represented by the diagonal of a constructed parallelogram?
The diagonal is the resultant, or sum, of two vectors.
What is the resultant of a pair of one pound forces at right angles to each other?
The resultant is a force of 1.41 pounds in a direction bisecting the 90-degree angle between the two vectors.
What are the units for force?
Force can be expressed in newtons or pounds.
What is the net force on a bag pulled down by gravity with a force of 18 newtons and pulled upward by a rope with a force of 18 newtons?
The net force is zero newtons.
What does it mean to say something is in mechanical equilibrium?
An object in mechanical equilibrium experiences a zero net force.
State the equilibrium rule for forces in symbolic notation
ΣF = 0
Newton said that something was needed to change the motion of an object. A clear reading of his first law tells us that what is needed is ______.
a non-zero net force
Consider a book that weighs 15 N at rest on a flat table. How many newtons of support force does the table exert on the book?
15 newtons up
When you stand at rest on a bathroom scale, how does your weight compare with the support force from the scale?
Your weight is equal in magnitude and opposite in direction to the support force from the scale.
What is the net force when a pair of 5-N forces simultaneously act in the same direction on an object?
10 N
A bowling ball at rest is in equilibrium. Is the ball in equilibrium when it moves at constant speed in a straight-line path?
Yes, the bowling ball is in equilibrium because ΣF = 0.
What is the net force on an object in either static or dynamic equilibrium?
The net force is zero.
If you push on a crate with a horizontal force of 100 N and it slides at constant velocity, what is the magnitude and direction of the frictional force acting on the crate?
The frictional force on the crate is 100 N opposite the direction of motion.
Which of Newton’s laws does the equilibrium rule illustrate?
Newton’s first law
What concept was not understood in the 16th century when people couldn’t conceive of a moving Earth?
They did not understand inertia.
A bird sitting in a tree is traveling at 30 km/s relative to the faraway Sun. When the bird drops to the ground below, does it still move at 30 km/s, or does this speed become zero?
It continues to move at 30km/s relative to the Sun, but it has a speed of 0 km/s relative to the ground.
Stand next to a wall that travels at 30 km/s relative to the Sun. With your feet on the ground, you also travel at the same 30 km/s. Do you maintain this speed when your feet leave the ground? What concept supports your answer?
When you jump, you continue to move at 30 km/s due to your inertia.
How much support force acts on a 200-N girl standing on a weighing scale?
200 N
A force of gravity pulls downward on a book on a table. What force prevents the book from accelerating downward?
normal force
If you pull horizontally on a crate with a force of 200 N, it slides across the floor in dynamic equilibrium. How much friction is acting on the crate?
200
N
Galileo taught us that if you roll a ball along a level surface it will
keep rolling if friction is absent.
A hockey puck is set in motion across a frozen pond. If ice friction and air resistance are neglected, the force required to keep the puck sliding at constant velocity is
equal to its weight.
equal to its weight divided by its mass.
equal to its mass times its weight.

****none of the above****

A hockey puck sliding across the ice finally comes to rest because
of friction.
The amount of force needed to sustain motion of a rock in outer space is
a force less than its weight if friction is absent.
a force equal to its weight.

****none of these****

Whirl a rock at the end of a string and it follows a circular path. If the string breaks, the tendency of the rock is to
When you flick a card from beneath a coin that hardly moves, you’re illustrating
inertia.
While you are standing in the aisle of a bus, the driver suddenly makes a left turn. You lurch to the right due to
your tendency to keep moving forward.
The resultant of a 40-N force at right angles to a 30-N force is
50 N.
When Nellie Newton hangs by the ends of a rope draped over a large pulley, the tension in each supporting vertical strand is
half her weight
The net force on any object in equilibrium is
zero.
Earth continually moves about 30 km/s through space, which means the wall you stand next to also is moving at 30 km/s. When you jump vertically the wall doesn’t slam into you because
you’re moving horizontally just as fast as the wall.
If you toss a coin straight upward while in a train moving at constant velocity, the coin will land
as if you were at rest.
The force that causes Earth to orbit the Sun is due to gravity, while the force needed to keep Earth moving as it circles the Sun is
no force at all.
An object in mechanical equilibrium is an object
moving with constant velocity.
having no changes in velocity.
at rest.

****all of the above****

Inertia is defined as a
property of matter.
When no forces act on moving objects their paths are normally
straight lines.
Monkey Mo hangs from the middle of a horizontal rope. Tension in the rope is greatest if the rope
sags very little.