chapter2 Flashcards
What relationship between the Sun and Earth did Copernicus formulate?
The Earth revolved in a circle about the Sun.
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.
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
What is the net force when a pair of 5-N forces simultaneously act in the same direction on an object?
10 N
Which of Newton’s laws does the equilibrium rule illustrate?
Newton’s first law
If while riding in a smooth-riding train, you toss a coin upward, the coin will normally land ______.
in your hand
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 does it mean to say something is in mechanical equilibrium?
An object in mechanical equilibrium experiences a 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 N up
The earliest and most influential Greek philosopher was Aristotle, who among many contributions taught that
- the four elements are earth, water, air, and fire.
- violent motion requires a sustained push or pull.
- all motion is either natural or violent.
Science later greatly advanced when Galileo favored
experiment over philosophical discussions.
The first scientist to introduce the concept of inertia was
galileo
Inertia is defined as a
property of matter
If no external forces act on a moving object, it will
continue moving at the same speed.
When no forces act on moving objects their paths are normally
straight lines
If gravity between the Sun and Earth suddenly vanished, Earth would continue moving in
a straight-line path.
A package falls off a truck that is moving at 30 m/s. Neglecting air resistance, the horizontal speed of the package just before it hits the ground is
about 30 m/s.
When a rocket ship gaining speed in outer space runs out of fuel, it
no longer gains speed
A moving van with a stone lightly glued to the midpoint of its ceiling smoothly moves at constant velocity. When the glue gives way, the stone falls and hits the floor
exactly below the midpoint of the ceiling.
Two students engaged in a tug-of-war each pull a rope in opposite directions with a force of 400 N. The net force on the rope is
zero and rope tension is 400 N.
A force is a vector quantity because it has both
magnitude and direction.
Which of the following is a vector quantity?
none
A block pulled to the left with 15 N and to the right with 5 N at the same time experiences a net force of
10 N
When a pair of 10-N forces act on a box of candy, the net force on the box is
Any of the above depending on the directions of forces
The resultant of a 40-N force at right angles to a 30-N force is
50N
The net force on any object in equilibrium is
zero
The equilibrium rule, F = 0, applies to
- objects or systems at rest.
- objects or systems in uniform motion in a straight line
The equilibrium rule applies to
vector quantities
The force of friction on a sliding object is 10 N. The applied force needed to maintain a constant velocity is
10N
The support force on a 10-N book at rest on a table is
10N
The support force on a 30-kg dog sleeping on the floor is
about 300 N.
A gymnast performing somersaults in a high-flying plane moving at constant velocity needs to make
no adjustments
A bird sitting on the limb of a tree is moving about 30 km/s with respect to the Sun. If the bird takes 1 second to drop down to a worm below, the worm would be 30 km downrange from the bird when it reached the ground. This faulty reasoning is best countered with Newton’s
law of inertia
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.
Which of the following is a vector quantity?
- acceleration
- momentum
- velocity
- displacement
- force
The amount of force needed to sustain motion of a rock in outer space is
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
follow a straight-line path.
When you flick a card from beneath a coin that hardly moves, you’re illustrating
inertia
Nellie pulls with a force of 50 N on a horizontal rope tied to a tree at rest. The net force on the rope is
zero and rope tension is 50 N.
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 Nellie hangs from a horizontal bar that is supported by four vertical ropes, the tension in the ropes
add to equal her weight
When you stand at rest on a pair of bathroom scales, the reading on each scale
add up to equal your weight
Galileo taught us that if you roll a ball along a level surface it will
keep rolling if friction is absent.
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
