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 ii objects that have made contact (usually) with each other. As in any interaction, a standoff results in a force being applied to the 2 colliding objects. Newton's laws of motion govern such collisions. In the second unit of The Physics Classroom, Newton's third police force of motion was introduced and discussed. Information technology was said that...

... in every interaction, there is a pair of forces interim on the two interacting objects. The size of the forcefulness on the first object equals the size of the forcefulness on the second object. The management of the forcefulness on the first object is contrary to the direction of the force on the 2d object. Forces always come up in pairs - equal and opposite action-reaction strength pairs.

Newton's Laws Applied to Collisions

Newton's 3rd constabulary of motion is naturally applied to collisions between ii objects. In a collision between two objects, both objects experience forces that are equal in magnitude and opposite in direction. Such forces often cause one object to speed upwardly (proceeds momentum) and the other object to boring downward (lose momentum). According to Newton'due south tertiary law, the forces on the ii objects are equal in magnitude. While the forces are equal in magnitude and contrary in direction, the accelerations of the objects are not necessarily equal in magnitude. In accord with Newton'due south 2nd constabulary of move, the acceleration of an object is dependent upon both forcefulness and mass. Thus, if the colliding objects have unequal mass, they will accept unequal accelerations equally a outcome of the contact force that results during the collision.

Consider the standoff between the club head and the golf 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 by the club head is equal to the force experienced past the golf ball. Virtually observers of this collision have difficulty with this concept because they perceive the loftier speed given to the ball as the outcome of the collision. They are not observing unequal forces upon the ball and club head, but rather unequal accelerations. Both guild head and brawl experience equal forces, all the same the brawl experiences a greater acceleration due to its smaller mass. In a collision, in that location is a force on both objects that causes an acceleration of both objects. The forces are equal in magnitude and opposite in management, however the to the lowest degree massive object receives the greatest acceleration.

Consider the standoff between a moving seven brawl and an eight ball that is at rest in the sport of table pool. When the 7 brawl collides with the viii ball, each ball experiences an equal force directed in opposite directions. The rightward moving seven ball experiences a leftward force that causes information technology to slow downwards; the eight brawl experiences a rightward force that causes it to speed up. Since the two balls have equal masses, they will also feel equal accelerations. In a standoff, there is a force on both objects that causes an dispatch of both objects; the forces are equal in magnitude and opposite in direction. For collisions between equal-mass objects, each object experiences the same acceleration.

Consider the interaction between a male and female person figure skater in pair figure skating. A woman (thousand = 45 kg) is kneeling on the shoulders of a human being (m = 70 kg); the pair is moving along the water ice at 1.five m/s. The human gracefully tosses the adult female frontward through the air and onto the water ice. The adult female receives the forward strength and the man receives a backward force. The force on the man is equal in magnitude and reverse in direction to the force on the woman. Yet the acceleration of the adult female 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 backward force. "Later all," they might contend, "the homo did not move backward." Such observers are presuming that forces cause motion. In their minds, a backward strength on the male skater would cause a astern motility. This is a common misconception that has been addressed elsewhere in The Physics Classroom. Forces crusade acceleration, not motion. The male figure skater experiences a backwards force that causes his backwards acceleration. The male person skater slows down while the adult female skater speeds upward. In every interaction (with no exception), there are forces interim upon the two interacting objects that are equal in magnitude and opposite in direction.

Collisions are governed past Newton's laws. The police of activity-reaction (Newton's third constabulary) explains the nature of the forces between the two interacting objects. According to the law, the force exerted past object i upon object two is equal in magnitude and opposite in direction to the forcefulness exerted by object 2 upon object i.

Check Your Understanding

Express your agreement of Newton'due south 3rd law by answering the following questions. Click the button to bank check your answers.

1. While driving down the road, a firefly strikes the windshield of a omnibus and makes a quite obvious mess in front of the confront of the driver. This is a clear case of Newton's third law of motion. 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 bus?

2. For years, space travel was believed to be impossible because at that place was nothing 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 infinite is because ...

a. infinite is void of air so the rockets accept nothing to push button off of.

b. gravity is absent in space.

c. space is void of air and and then in that location 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 rifle recoils when fired. This recoil is the upshot of action-reaction forcefulness pairs. A gunpowder explosion creates hot gases that expand outward allowing the rifle to push frontwards on the bullet. Consistent with Newton's tertiary law of motion, the bullet pushes backwards upon the burglarize. The acceleration 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.

4. Kent Swimm, who is taking Physics for the third year in a row (and non because he likes information technology), has rowed his boat within 3 feet of the dock. Kent decides to bound onto the dock and plough around and dock his boat. Explain to Kent why this docking strategy is not a adept strategy.

5. A clown is on the ice rink with a large medicine ball. If the clown throws the ball forward, so he is set up into backwards motion with the same momentum as the ball's forward momentum. What would happen to the clown if he goes through the motility of throwing the ball without actually letting go of information technology? Explain.

6. Dale, Mel, and Shanelle are astronauts on a spaceship. They each have the same mass and the aforementioned strength. Dale and Mel decide to play catch with Shanelle, intending to throw her back and forth between them. Dale throws Shanelle to Mel and the game begins. Describe the motion of Dale, Mel and Shanelle every bit the game continues. If we assume that each throw involves the same amount of button, then how many throws volition the game last?