physics ch 7
Terms in this set (42)
can an action force exists without a reaction force?
when a hammer exerts a force on a nail, how does this amount of force compare with that of the nail on the hammer?
they are equal forces
Newtons third law of motion
whenever one object exerts a force on a second object the second exerts an equal and opposite force on the first
consider hitting a baseball with a bat. if we call the force the bat exerts against the ball the action force, what is the reaction force?
the force the ball exerts on the bat
if a bat hits a ball with 1000N of force, can the ball exert less than 1000N of force on the ball? more than 1000N?
it would be equal- whatever the bat does to the ball, the ball does to the bat
when you rub your hands together can you push harder on one hand than the other?
your weight is the result to the gravitational force of earth on your body. What is the corresponding reaction force?
me pulling up on the earth, the earth pulling down on me
why can you exert greater force on the pedals of a bicycle if you pull up on the handlebars?
if you pull up, the handle bars will push down on you
consider the two forces that act on a person standing, the downward force of gravity and the upward force of the floor. are these forces equal and opposite?
they are not a action reaction pair because there are 3 objects not two, earth and the floor aren't acting on each other only on person. the floor and earth are acting on a 3rd obj
if you walk on a log that is floating and the log moves backwards. why?
your feet push back on the log
why is it easier to walk on carpet floor instead of tile?
there is friction
if you step off a ledge you accelerate noticeably toward the earth. does the earth accelerate toward you?
yes because opposite forces are equal
what is the action reaction pair when a racquet hits a tennis ball neglecting air resistance?
earth pulls on the ball, the ball pulls on the earth
say you're weighing yourself an you push down on a sink and another guy pushes up what are the action reaction pairs?
you push down on the sink it pushes up on you
you pull up on the sink it pushes down on you
when a gin fires why does the bullet leave the barrel at a high speed and the gin move slightly?
action reaction pair: bullet and gun
gun pushes bullet out and bullet pushes gun back.
the force is inside the gun and masses are different
smaller the mass, the more acceleration
in a tug of war if the action is you pulling on the rope, what is the reaction force? ground pushing back on you or opponent pulling back on rope?
neither of these because reaction is the rope pulling on you
is a rocket propelled by the impact of exhaust gases against the atmosphere?
no bc everything happens inside the rocket. the rocket pushes gas out so the gas pushes on the rocket
what are the action reaction forces of an air plane and a bird?
airplane exerts a downward force on the air and air exerts upward force
bird exerts downward force on air and air exerts upward force on the wings
if the world pulls you downward against your chair, what is the reaction force?
chair is in the way, you pull the wool up
when a cannon is fired, are the forces on the cannonball and on the cannon equal in magnitude? are the accelerations of the two equal?
accelerations aren't equal- smaller mass more acceleration
forces are equal
when a cannon ball is fired, why do the ball and the cannon have different accelerations?
smaller mass more acceleration- ball is smaller
identify the force that propels a rocket
burnt fuel propels it
if action equals reaction why isn't earth pulled into orbit around a communication satellite?
the satellite has smaller mass so it doesn't accelerate
a small car bumps into a van at rest. which vehicle is the force of impact greater on? which vehicle undergoes the greater change in acceleration?
the force of impact is the same but the smaller car has the most acceleration
what force propels a rocket when it is in a vacuum?
fuel propels the rocket
since the force that acts on a cannonball when a cannonball is fired is equal and opposite to the force that acts on the cannon does this imply a zero net force
no because the force is acting in two different directions
when a net force is exerted on a system the system will accelerate but when an applied force and its reaction are within a system the system as a whole doesn't accelerate. (true or false)
why doesn't the interatomic forces from the inside of a baseball accelerate the ball?
because internal forces don't move
is it possible for two people to pull on a horizontal rope with two scales at the end and have them read different??
no because when they differ acceleration will take hold and the heavier person will win and the lighter will fall along with the rope
is a man with two horses in each hand tied to a rope balanced?
yes tension is balanced
is a man with a rope tied to a tree in one hand and a horse in the other balanced?
yes tension is balanced
is the man with a rope in his hand tied to a tree and in the other hand tied to two horses balanced?
no it has twice the tension
if a balloon is floating in the air and a balloonist climbs up the rope which direction will the ballon go?
opposite because of newtons third law
when you get up from a sitting positioned do your feet push against the floor with a greater equal or less force than your weight?
your accelerating so there is a net force so force is more than your weight
when a weight lifter jerks a barbell over his head, is the force exerted on the barbell more than less than or equal to the barbells weight?
greater than because he is exerting more force then the barbell
identify two action reaction forces that exist while standing on a scale
you exert a force on the scale and the scale exerts a force on you
gravity pushes down on you and you push down on gravity
whatever one object exerts the other is the same
why would a person trying to walk on ice not have a forward motion?
the ice can't push back on you
no friction or reaction force
why is it that when a boulder falls off a cliff toward the ground, earth accelerates the boulder and we don't feel it?
earths huge mass causes acceleration to be infinitesimally small
what are the three factors that you must consider in order to understand why a cannon ball moves faster than than the cannon when its shot
mass acceleration and force
internal forces _______ _____
describe the horse cart problem?
the horse pulls on the cart and the cart pulls equal on the horse so there cant be any acceleration
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