# Mr.McCormick – Physics Chapter 2

Flashcard maker : Lily Taylor
Every object in the universe has a proper place determined by a combination of
four elements
– fire
– water
– earth
– air
Any object not in its proper place will
strive to get there
Natural motion
– Straight up or straight down for all things on Earth
– Beyond Earth, motion is circular
Violent motion
Produced by external pushes or pulls on objects
Galileo’s discovery
– Objects of different weight fall to the ground at the same time in the absence of air resistance.
– A moving object needs no force to keep it moving in the absence of friction.
Galileo presented the __________ theory intead of the geocentric theory
heliocentric
Force
a push or pull
Inertia
– is a property of matter to resist changes in motion.
– depends on the amount of matter in an object
If the ball comes to rest, it is not due to its “nature,” but due to
friction
Balls rolling on downward-sloping planes
pick up speed
Balls rolling on upward-sloping planes
loose speed
The use of inclined planes for Galileo’s experiments helped him to
discover the property called inertia
An object continues to do whatever it happens to be doing unless a
force is exerted upon it
Small object with a lot of acceleration =
a lot of force
Vector quantity
– a quantity whose description requires both magnitude (how much) and direction (which way)
– can be represented by arrows drawn to scale, called vectors
length of arrow represents
Net force
the combination of all forces that act on an object
A cart is pulled to the right with a force of 15 N while being pulled to the left with a force of 20 N. The net force on the cart is
5 N to the left
Scalar quantity
has magnitude
Resultant
The sum of two or more vectors
For vectors in the same direction
For vectors in opposite directions
subtract arithmetically
Two vectors that don’t act in the same or opposite direction
use parallelogram rule
Two vectors at right angles to each other
use Pythagorean Theorem
The vector sum of forces acting on a nonaccelerating object equals
zero
The equilibrium rule applies to
vector quantities
Support force (normal force)
is an upward force on an object that is opposite to the force of gravity
When you stand on two bathroom scales with one foot on each scale and with your weight evenly distributed, each scale will read
Equilibrium
a state of no change with no net force acting
Static equilibrium (example)
hockey puck at rest on slippery ice
Dynamic equilibrium (example)
hockey puck sliding at constant
speed on slippery ice
Equilibrium test
whether something undergoes change in motion
A bowling ball is in equilibrium when it
– is at rest
– moves steadily in a straight-line path
You push a crate at a steady speed in a straight line. If the friction force is 75 N, how much force must you apply
Equal to 75 N
Copernicus proposed that
Earth was moving, circulating the Sun
If Earth moved, how could a bird swoop from a branch to catch a worm
As it swoops, due to inertia, it continues to move sideways at the speed of Earth along with the tree, worm, etc.
You are riding in a vehicle at a steady speed and toss a coin straight upward. Where will the coin land
Aristotle and his followers for many centuries thought Earth was at rest at the center of the universe because
humans experience no sensation of a moving Earth
Science greatly advanced when Galileo favored
experiment over philosophical discussions
Galileo said that if you rolled a ball along a level surface it would
soon slow down due to its natural tendency to come to rest.
When Galileo rolled a ball down one incline so that at the bottom it rolled up another, he found that the ball rolled
almost to its initial height.
According to Galileo, inertia is a
property of all matter
When dishes remain on a table when you yank away a tablecloth, you’re illustrating
inertia
If gravity between the Sun and Earth suddenly vanished, Earth would continue moving in
a straight-line path
A space probe in remote outer space continues moving
even though no force acts on it
Consider a ball resting in the middle of a cart. When you quickly jerk the cart forward, the ball
hits the back of the cart.
A girl pushes a cart to the left with a 100-N force. A boy pushes it to the right with a 50-N force. The net force exerted by the girl and the boy is
50 N to the left.
When a 10-kg block is simultaneously pushed eastward with a force of 20 N and westward with 15 N, the combination of these forces on the block is
5 N east.
When a 10-N object is suspended at rest by two vertical strands of rope, the tension in each rope is
5 N
When sign painters Burl and Paul stand on opposite ends of a scaffold, the tensions in the two supporting ropes
depend on the relative weights of Burl and Paul
If Burl carried Paul piggy-back while standing in the middle of a scaffold, the tensions in the two supporting ropes would
be equal
Burl and Paul have a total weight of 1300 N. The tensions in the ropes that support the scaffold they stand on add to 1700 N. The weight of the scaffold itself must be
400 N
If the ropes that support Paul and Burl were not vertical, but at an angle, rope tensions would be
greater
A box pulled north with 60 N of force, while being pulled east with 80 N of force, has a resultant of
100 N
Place a book that weighs 10 N on a table and the support force on the book is
10 N
The equilibrium rule, ΣF = 0, applies to
objects or systems at rest
objects or systems in uniform motion in a straight line
The net force on any object in equilibrium is
zero
Earth moves about 30 km/s relative to the Sun. When you jump upward in front of a wall, the wall doesn’t slam into you at 30 km/s. This is because the wall
and you are moving at the same horizontal speed before, during, and after your jump