# Shared Flashcard Set

## Details

PHYSICS
Chapters 2-4
55
Physics
01/20/2018

Term
 What keeps asteroids moving in space?
Definition
 Nothing keeps them moving. The Sun can deflect their path, but it isn't needed to keep them moving.
Term
 What does a car whiplash have to do with Newton's first law?
Definition
 Your head and body remains at rest, but when you move forward, only your back seat keeps you from moving, so the head will continue to move because of the force that is acted upon it
Term
 What law applies to when you move forward/backward on a bus when accelerating and why?
Definition
 Newton's first law because when the bus is at rest, you are at rest. So when the bus moves, you are being pulled with it and results in your body moving backwards.
Term
 What can you say correctly about a pair of vectors that add together to equal 0?
Definition
 The vectors are equal in magnitude and opposite in direction
Term
 A bird sits on a clothes line. Will the tension be greater if the line sags a little or a lot?
Definition
 A little because larger vectors are needed to support the weight of the bird.
Term
 Can an object be in mechanical equilibrium if a single non-zero force acts upon it?
Definition
 No because its motion will change
Term
 If you pull horizontally on a crate with a force of 200N, it slides across the floor in dynamic equilibrium. How much friction is acting upon the crate?
Definition
 200 N (equal to your pull of -200N)
Term
 A parachutist is falling through the sky in dynamic equilibrium. How do the magnitude of the gravitational pull and air resistance compare?
Definition
 They're equal, so the net force is zero.
Term
 A ball rolling on the floor moves slightly slower over time. Does this violate Newton's first law? Why or why not?
Definition
 No, because the force of air resistance is acting up on it. If there was no force acting upon the ball, it will continue to roll.
Term
 Since the earth is moving, you move with it and won't hit the wall in your room. But when you jump, how come you don't hit the wall since the earth is still moving?
Definition
 Because your body is in motion so it will stay in motion.
Term
 Is a fine for speeding based on your instantaneous speed or your average speed? Explain
Definition
 Instantaneous speed because that's the speed registered on the speedometer gun the police are using.
Term
 Light travels in a straight line at a constant speed of 300,000 km/s. What is its acceleration?
Definition
 Zero because a constant velocity means no acceleration.
Term
 You are driving on a highway, then w/o changing speed, you turn on a curve. (a) Does your velocity change? (b) Do you accelerate? Explain
Definition
 (a) Yes, because of the change in direction (b) Yes, because the velocity changes
Term
 For a free-falling object dropped at rest, what is the acceleration of the object after 5 seconds? After 10 seconds?
Definition
 The acceleration is the same as g (gravity) at any point in the fall because it is a free fall.
Term
 Suppose that a free-falling object is equipped with a speedometer. How much speed is increased with each second of the object falling?
Definition
 10 m/s each second (because of gravity)
Term
 If there was no air resistance, why would it be dangerous to go outside when it's raining?
Definition
 If not for the slowing affect of air resistance, the raindrops will strike the ground with speed as high as bullets.
Term
 When a ball is tossed into the air with air resistance, how does the return speed compare with its initial speed?
Definition
 Air resistance decreases speed, so a ball will return with less speed than it did initially.
Term
 How does a speedometer indicate whether or not and object is accelerating?
Definition
 When the speed changes. No change = no acceleration
Term
 If gold was sold by weight, would you buy it in Death Valley or Denver? If it was sold by mass, where would you buy it?
Definition
 If by weight, buy it in Denver because the force of gravity is lesser there. If by mass, it would be the same price both places.
Term
 If your empty hand hits a wall, it will hurt less. But if you're holding an object and hit a wall, it will hurt more. Why? Which of Newton's laws applies here?
Definition
 Holding an object means there's more mass. More mass means there's more tendency to keep moving. Newton's first law.
Term
 When blocking in football, a lineman wants to get lower than their opponent when pushing each other to lift them off the ground.   What effect does this have on the friction force between the opposing linemen's feet and the ground?
Definition
 Lifting the opponent decreases the force with which the ground supports him = decreases the force of friction he can muster.
Term
 (a) Is a skydiver who has reached terminal speed in free fall? (b) Is a satellite circling above Earth's atmosphere in free fall?
Definition
 (a) No, because there is air resistance. Free fall means free of all forces except gravity. (b) Yes, even though the satellite isn't getting any closer to Earth, it is still falling.
Term
 Two balls fall from the same height. One is filled with lead pellets. Which one will hit the ground first? Which one has a greater air resistance?
Definition
 The ball with lead pellets will hit the ground first. The ball with the lead pellets also has the greatest air resistance because it is falling much faster than the normal ball.
Term
 What is Inertia?
Definition
 The property of things to resist change in motion
Term
 What's Newton's first law of motion?
Definition
 An object at rest stays at rest unless acted upon by a force
Term
 What is a Force?
Definition
 A push or pull
Term
 What is a Net Force?
Definition
 The vector sum of forces acting upon an object
Term
 What is a Vector?
Definition
 An arrow that represents a vector quantity
Term
 What is a Vector Quantity?
Definition
 Having both magnitude and direction (Ex: force)
Term
 What is a Scalar Quantity?
Definition
 A quantity that has magnitude but no direction
Term
 What is an example of Scalar Quantity?
Definition
 Mass, volume, time, speed
Term
 What is an example of Vector Quantity?
Definition
 Force, velocity, acceleration
Term
 What is a Resultant?
Definition
 The net result of a combination of 2 or more vectors
Term
 What is Mechanical Equilibrium?
Definition
 When the net force on an object is zero
Term
 What is the Equilibrium Rule?
Definition
 On an object or system of objects in mechanical equilibrium, the sum of forces = zero (∑F = 0)
Term
 What relationship between the Earth and the Sun did Copernicus formulate?
Definition
 That the Earth revolves around the Sun, not the other way around
Term
 What did Galileo discover in his Leaning Tower of Pisa experiment?
Definition
 Objects with different weight still hit the ground at the same time
Term
 How fast are you moving relative to the Sun?
Definition
 30 km/s
Term
 What is Speed?
Definition
 How fast an object moves; the distance traveled per unit of time
Term
 What is Average Speed?
Definition
 The total distance traveled divided by time of travel
Term
 What is a Velocity?
Definition
 An object's speed and direction of motion
Term
 What is Acceleration?
Definition
 The rate at which velocity changes with time
Term
 What is a Free Fall?
Definition
 Motion under the influence of gravity only
Term
 What is a Force?
Definition
 A push or pull exerted on an object
Term
 What is Force measured in?
Definition
 Newtons
Term
 What is Friction?
Definition
 The force that normally opposes the motion of an object
Term
 What is Mass?
Definition
 The amount of matter in an object
Term
 What is Weight?
Definition
 Force due to gravity on an object
Term
 What is Terminal Speed?
Definition
 The point where the resistance of air matches the pull of gravity
Term
 Is acceleration proportional to the net force, or does acceleration equal net force?
Definition
 Proportional
Term
 What is Static Friction?
Definition
 When force is applied to an object but it doesn't move
Term
 What is Kinetic Friction?
Definition
 When force is applied to an object and it moves
Term
 What affects the amount of air resistance (3)?
Definition
 Speed, size, and shape
Term
 What is Earth's gravitational pull?
Definition
 9.8 m/s² or 10/ms²
Term
 What is the moon's gravitational pull?
Definition
 1.6 m/s² or 2 m/s²
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