Mr.McCormick – Physics Chapter 2 – Flashcards
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Every object in the universe has a proper place determined by a combination of
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four elements - fire - water - earth - air
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Any object not in its proper place will
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strive to get there
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Natural motion
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- Straight up or straight down for all things on Earth - Beyond Earth, motion is circular
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Violent motion
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Produced by external pushes or pulls on objects
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Galileo's discovery
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- 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.
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Galileo presented the __________ theory intead of the geocentric theory
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heliocentric
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Force
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a push or pull
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Inertia
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- is a property of matter to resist changes in motion. - depends on the amount of matter in an object
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If the ball comes to rest, it is not due to its "nature," but due to
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friction
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Balls rolling on downward-sloping planes
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pick up speed
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Balls rolling on upward-sloping planes
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loose speed
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The use of inclined planes for Galileo's experiments helped him to
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discover the property called inertia
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An object continues to do whatever it happens to be doing unless a
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force is exerted upon it
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Small object with a lot of acceleration =
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a lot of force
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Vector quantity
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- a quantity whose description requires both magnitude (how much) and direction (which way) - can be represented by arrows drawn to scale, called vectors
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length of arrow represents
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magnitude and arrowhead shows direction
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Net force
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the combination of all forces that act on an object
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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
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5 N to the left
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Scalar quantity
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has magnitude
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Resultant
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The sum of two or more vectors
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For vectors in the same direction
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add arithmetically
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For vectors in opposite directions
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subtract arithmetically
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Two vectors that don't act in the same or opposite direction
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use parallelogram rule
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Two vectors at right angles to each other
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use Pythagorean Theorem
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The vector sum of forces acting on a nonaccelerating object equals
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zero
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The equilibrium rule applies to
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vector quantities
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Support force (normal force)
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is an upward force on an object that is opposite to the force of gravity
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When you stand on two bathroom scales with one foot on each scale and with your weight evenly distributed, each scale will read
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half your weight
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Equilibrium
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a state of no change with no net force acting
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Static equilibrium (example)
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hockey puck at rest on slippery ice
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Dynamic equilibrium (example)
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hockey puck sliding at constant speed on slippery ice
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Equilibrium test
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whether something undergoes change in motion
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A bowling ball is in equilibrium when it
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- is at rest - moves steadily in a straight-line path
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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
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Equal to 75 N
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Copernicus proposed that
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Earth was moving, circulating the Sun
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If Earth moved, how could a bird swoop from a branch to catch a worm
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As it swoops, due to inertia, it continues to move sideways at the speed of Earth along with the tree, worm, etc.
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You are riding in a vehicle at a steady speed and toss a coin straight upward. Where will the coin land
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In your hand
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Aristotle and his followers for many centuries thought Earth was at rest at the center of the universe because
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humans experience no sensation of a moving Earth
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Science greatly advanced when Galileo favored
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experiment over philosophical discussions
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Galileo said that if you rolled a ball along a level surface it would
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soon slow down due to its natural tendency to come to rest.
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When Galileo rolled a ball down one incline so that at the bottom it rolled up another, he found that the ball rolled
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almost to its initial height.
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According to Galileo, inertia is a
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property of all matter
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When dishes remain on a table when you yank away a tablecloth, you're illustrating
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inertia
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If gravity between the Sun and Earth suddenly vanished, Earth would continue moving in
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a straight-line path
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A space probe in remote outer space continues moving
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even though no force acts on it
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Consider a ball resting in the middle of a cart. When you quickly jerk the cart forward, the ball
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hits the back of the cart.
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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
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50 N to the left.
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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
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5 N east.
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When a 10-N object is suspended at rest by two vertical strands of rope, the tension in each rope is
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5 N
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When sign painters Burl and Paul stand on opposite ends of a scaffold, the tensions in the two supporting ropes
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depend on the relative weights of Burl and Paul
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If Burl carried Paul piggy-back while standing in the middle of a scaffold, the tensions in the two supporting ropes would
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be equal
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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
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400 N
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If the ropes that support Paul and Burl were not vertical, but at an angle, rope tensions would be
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greater
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A box pulled north with 60 N of force, while being pulled east with 80 N of force, has a resultant of
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100 N
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Place a book that weighs 10 N on a table and the support force on the book is
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10 N
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The equilibrium rule, ΣF = 0, applies to
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objects or systems at rest objects or systems in uniform motion in a straight line
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The net force on any object in equilibrium is
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zero
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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
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and you are moving at the same horizontal speed before, during, and after your jump
