PHYS 1210: Ch. 5 & 8 – Newton’s 3rd Law and Circular Motion
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What is meant by tangential speed?
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It is the description of how fast a point or object on a circle or circular object is moving at a certain distance from the center.
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When you whirl a can at the end of a string in a circular path, what is the direction of the force you exert on the can?
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The force is inward towards the center.
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Is it an inward force or an outward force that is exerted on the clothes during the spin cycle of an automatic washing machine?
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It is an inward force that is exerted.
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If the string that holds a whirling can in its circular path breaks, what kind of force causes it to move in a straight-line path - centripetal, centrifugal, or no force? What law of physics supports your answer?
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There is no force. The law that supports my answer is Newton's First Law; \"any object at rest or in motion stays at rest or in motion, unless acted upon by an outside force\".
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If you are in a car that rounds a curve, and you are not wearing a seat belt, and you slide across your seat and slam against a car door, what kind of force is responsible for your slide - centripetal, centrifugal, or no force? Why is the correct answer \"no force\"?
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The is no force responsible for my slide. Since I am in the car and there was a centripetal force that was applied to the car, the car slid out from under me.
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How can gravity be simulated in an orbiting space station?
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By spinning a cylinder to create a centrifugal force.
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When you are in the front passenger seat of a car turning to the left, you may find yourself pressed against the right-side door. Why do you press against the door? Why does the door press on you? Does your explanation involve a centrifugal force, or Newton's laws?
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My answer involves Newton's First Law and centrifugal force. Newton's First Law because an object, person in the car, in motion stays in motion. Centrifugal because of the change in direction; the body is going with the car as it turns. Both of these are reasons to why one presses against the door.
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When you push against a wall, what pushes back?
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The wall
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When hitting a tennis ball with your racquet, the force on the ball has the same magnitude as the force on the _______.
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Racquet
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A Volkswagen bug and a Volvo truck have a head-on collision. Which statement is true?
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The magnitudes of both forces are the same.
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A boxer can hit a heavy bag with great force. Why can't he hit a piece of tissue paper in midair with the same amount of force?
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the mass of the paper doesnt match the mass of the punch. if you look up newtons 3rd law, every action has a reaction therefore the boxer will be able to punch the paper only is the force of the punch is equal or greater than the force that exerts back the paper
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Consider hitting a baseball with a bat. If we call the force on the bat by the ball the action force, identify the reaction force.
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The reaction force is the backward force on the bat due to the ball
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Earth pulls down on you with a gravitational force that you call your weight. Do you pull up on Earth with the same amount of force? Explain using Newton's 3rd Law.
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Yes. This is because we are pushing on the Earth the same amount of force that it is pushing back on us. The forces are of equal and opposite nature.
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If the forces that act on a cannonball and the recoiling cannon from which it is fired are equal in magnitude, why do the cannonball and cannon have very different accelerations?
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The cannonball and the cannon may have equal magnitude but they may not have equal mass. This is the imbalance that causes the difference in acceleration according to Newton's Second law.
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How does a helicopter get its lifting force?
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It gets its lifting force from the air being forced downward due to the propeller (the action), and (the reaction) the air pushes back forcing the helicopter to be lifted upward.
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Can you physically touch a person without that person touching you with the same amount of force?
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No, it's Newton's 3rd Law: if you push something it will push back with equal force.
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When you rub your hands together, can you push harder on one hand than the other?
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No, each hand pushes equally against the other which falls under Newton's 3rd Law.
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Identify action and reaction forces in this interaction: Part A A hammer hits a nail. Part B Earth gravity pulls down on a book. Part C A helicopter blade pushes air downward.
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Part A Action- the hammer hitting the nail Reaction- the nail hitting the hammer Part B Action- Earth pulls down on the book Reaction- The book pulls the Earth up Part C Action- Blades push air downward Reaction- the force in return pushes the helicopter upward.
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You hold an apple over your head.: Part A Identify all the forces acting on the apple and their reaction forces. Part B When you drop the apple, identify all the forces acting on it as it falls and the corresponding reaction forces. Neglect air drag.
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Part A The acting force on the apple is that it is pulled down by Earth, therefore the reaction is the apple pulling up on the Earth. So when the hand pushes the apple upward (action) the apple pushes the hand downward (reaction). Part B The apple is in free fall and the only force acting on it is its weight pulling it down.
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If you drop a rubber ball on the floor, it bounces back up. What force acts on the ball to provide the bounce?
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The force of the floor reacting to the ball bouncing on it provides the bonce of the ball.
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Why does a rope climber pull downward on the rope to move upward?
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The climber pulls downward so that the rope can pull him upward. It is a action reaction situation where by pulling down the climber is helping them self to move up the rope.
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If a Mack truck and Honda Civic have a head-on collision, upon which vehicle is the impact force greater? Which vehicle experiences the greater deceleration? Explain your answers.
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The impact force of each will be the same. The greater deceleration would be based on the different masses between the truck and the car. The truck won't have as much deceleration as the Civic because it is bigger in size and has more mass.
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Ken and Joanne are astronauts floating some distance apart in space. They are joined by a safety cord whose ends are tied around their waists. If Ken starts pulling on the cord, will he pull Joanne toward him, or will he pull himself toward Joanne, or will both astronauts move? Explain.
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Both astronauts will move due to Newton's 3rd law. Since Ken is pulling Joanne towards him, the rope will react and pull him towards Joanne.
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Which of the following are scalar quantities, which are vector quantities, and which are neither? [Drag the appropriate items to their respective bins.] -Velocity -Age -Speed -Acceleration -Temperature
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Vector -Velocity -Acceleration Scalar -Speed -Age -Temperature Neither
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A boxer punches a sheet of paper in midair and brings it from rest up to a speed of 27 m/s in 0.054 s . [Express your answer to two significant figures and include the appropriate units.] Part A What acceleration is imparted to the paper? Part B If the mass of the paper is 0.003 kg, what force does the boxer exert on it? Part C How much force does the paper exert on the boxer?
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Part A a = m∆v/∆t = (25 m/s)/(0.05 s) = 500 m/s^2 Part B F = ma = m∆v/∆t = (0.003 kg)(25 m/s)/(0.05 s) = 1.5 N Part C By Newton's third law, the same amount, 1.5 N
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*Express your answer to two significant figures and include the appropriate units. Part A If you stand next to a wall on a frictionless skateboard and push the wall with a force of 32 N , how hard does the wall push on you? Part B If your mass is 74 kg , find your acceleration.
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Part A F = 32 N Part B a = 0.43 m/s^2
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An object following a straight-line path at constant speed
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has zero acceleration.
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A car travels in a circle with constant speed. The net force on the car is
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directed toward the center of the curve.
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An object following a circular path at constant speed
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has a net force acting upon it in the direction that is towards the center of its circular path.
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A car maintains a constant speed as it turns through a curve. The net force acting on a car is
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not zero, its direction is changing and this requires a unbalanced, net force to act on it.
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You twirl a ball on a string about in a circular path. The net force on the ball is
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directed toward your hand, the center of its path.
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You twirl about a ball on a string in a vertical circular path with a constant speed. What will be the direction the net force acting on the object at the bottom of its circular path?
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Upward, towards your hand.
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As a ball falls, the action force is the pull of Earth on the ball. The reaction force is the
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pull of the ball's mass on the Earth.
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A person is attracted toward the center of Earth by a 500-N gravitational force. The Earth is attracted toward the person with a force of
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500 N.
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A karate chop delivers a blow of 3000 N to a board that breaks. The force that acts on the hand during this event is
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3000 N.
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A skydiver falls towards the Earth. The attraction of the Earth on the diver pulls the diver down. What is the reaction to this force?
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-water resistance that will soon act upward on the diver -air resistance the diver encounters while falling -the attraction to the planets, stars, and every particle in the universe -all of these -NONE OF THESE
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A car traveling at 100 km/hr strikes an unfortunate bug and splatters it. The force of impact is
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the same for both.
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A vehicle that weights 400 N on the surface of the Earth is traveling in outer space at a speed of 400 m/s . It can be stopped by applying a constant force of 20 N for
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800 seconds
