How Can Two Objects of Different Sizes Exert the Same Amount of Force on Each Other?

The Law of Action-Reaction (Revisited)

A collision is an interaction between two objects that take made contact (usually) with each other. As in whatsoever interaction, a collision results in a force being practical to the two colliding objects. Newton'south laws of motion govern such collisions. In the 2d unit of measurement of The Physics Classroom, Newton'southward 3rd law of motion was introduced and discussed. It was said that...

... in every interaction, in that location is a pair of forces acting on the two interacting objects. The size of the force on the offset object equals the size of the strength on the second object. The direction of the forcefulness on the showtime object is contrary to the direction of the forcefulness on the 2nd object. Forces always come in pairs - equal and opposite action-reaction force pairs.

Newton's Laws Practical to Collisions

Newton'due south tertiary constabulary of motion is naturally applied to collisions between two objects. In a collision between two objects, both objects experience forces that are equal in magnitude and opposite in direction. Such forces oft cause one object to speed up (gain momentum) and the other object to boring down (lose momentum). Co-ordinate to Newton'southward third law, the forces on the 2 objects are equal in magnitude. While the forces are equal in magnitude and opposite in management, the accelerations of the objects are not necessarily equal in magnitude. In accord with Newton'south 2nd law of motion, the acceleration of an object is dependent upon both strength and mass. Thus, if the colliding objects have diff mass, they will take unequal accelerations every bit a issue of the contact force that results during the standoff.

Consider the standoff between the order head and the golf game ball in the sport of golf. When the club head of a moving golf club collides with a golf ball at rest upon a tee, the force experienced past the club head is equal to the force experienced by the golf ball. Well-nigh observers of this collision accept difficulty with this concept because they perceive the loftier speed given to the ball as the result of the collision. They are not observing diff forces upon the ball and society head, but rather unequal accelerations. Both society head and ball experience equal forces, even so the ball experiences a greater acceleration due to its smaller mass. In a collision, there is a force on both objects that causes an acceleration of both objects. The forces are equal in magnitude and opposite in direction, even so the least massive object receives the greatest acceleration.

Consider the collision between a moving vii brawl and an 8 brawl that is at remainder in the sport of table puddle. When the seven brawl collides with the eight brawl, each ball experiences an equal strength directed in opposite directions. The rightward moving seven ball experiences a leftward force that causes it to ho-hum downwards; the eight ball experiences a rightward force that causes it to speed upward. Since the two assurance have equal masses, they will also feel equal accelerations. In a collision, there is a force on both objects that causes an dispatch of both objects; the forces are equal in magnitude and contrary in direction. For collisions betwixt equal-mass objects, each object experiences the aforementioned dispatch.

 

Consider the interaction between a male and female figure skater in pair figure skating. A woman (m = 45 kg) is kneeling on the shoulders of a man (m = 70 kg); the pair is moving along the water ice at ane.5 m/due south. The human being gracefully tosses the woman forward through the air and onto the water ice. The woman receives the forward forcefulness and the man receives a backward force. The force on the man is equal in magnitude and opposite in management to the strength on the woman. All the same the dispatch of the woman is greater than the acceleration of the man due to the smaller mass of the woman.

Many observers of this interaction have difficulty believing that the human being experienced a astern forcefulness. "After all," they might argue, "the man did not motility backward." Such observers are presuming that forces crusade motility. In their minds, a backward strength on the male skater would cause a backward motion. This is a common misconception that has been addressed elsewhere in The Physics Classroom. Forces crusade dispatch, not motion. The male person figure skater experiences a backwards force that causes his backwards dispatch. The male person skater slows down while the woman skater speeds up. In every interaction (with no exception), there are forces acting upon the two interacting objects that are equal in magnitude and opposite in direction.

Collisions are governed by Newton'southward laws. The law of activeness-reaction (Newton'southward third police force) explains the nature of the forces betwixt the 2 interacting objects. According to the law, the force exerted past object 1 upon object two is equal in magnitude and opposite in direction to the force exerted by object ii upon object 1.

Bank check Your Understanding

Limited your understanding of Newton's third law by answering the following questions. Click the button to check your answers.

1. While driving down the route, a firefly strikes the windshield of a bus and makes a quite obvious mess in front of the confront of the driver. This is a clear case of Newton'south third law of movement. The firefly hit the bus and the bus hits the firefly. Which of the two forces is greater: the force on the firefly or the force on the omnibus?

2. For years, space travel was believed to be impossible considering there was nil that rockets could push button off of in space in order to provide the propulsion necessary to accelerate. This inability of a rocket to provide propulsion in space is because ...

a. space is void of air and then the rockets have zero to push off of.

b. gravity is absent in space.

c. space is void of air and and then at that place is no air resistance in space.

d. ... nonsense! Rockets do accelerate in space and take been able to do so for a long time.

three. Many people are familiar with the fact that a burglarize recoils when fired. This recoil is the upshot of action-reaction force pairs. A gunpowder explosion creates hot gases that expand outward allowing the rifle to push frontward on the bullet. Consequent with Newton's tertiary law of motion, the bullet pushes backwards upon the rifle. The dispatch of the recoiling rifle is ...

a. greater than the acceleration of the bullet.

b. smaller than the acceleration of the bullet.

c. the same size as the acceleration of the bullet.

 

four. Kent Swimm, who is taking Physics for the third year in a row (and not considering he likes it), has rowed his boat within 3 feet of the dock. Kent decides to leap onto the dock and turn effectually and dock his boat. Explain to Kent why this docking strategy is not a good strategy.

5. A clown is on the ice rink with a large medicine ball. If the clown throws the ball forwards, then he is ready into backwards move with the same momentum equally the ball's forward momentum. What would happen to the clown if he goes through the movement of throwing the ball without actually letting go of it? Explain.

 

6. Dale, Mel, and Shanelle are astronauts on a spaceship. They each have the same mass and the same forcefulness. Dale and Mel make up one's mind to play take hold of with Shanelle, intending to throw her back and along between them. Dale throws Shanelle to Mel and the game begins. Describe the motion of Dale, Mel and Shanelle as the game continues. If we assume that each throw involves the aforementioned amount of push, then how many throws will the game last?

 

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Source: https://www.physicsclassroom.com/class/momentum/Lesson-2/The-Law-of-Action-Reaction-%28Revisited%29

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