Newton’s Laws of Motion Number 3

Forces always occur in interacting force pairs. Newton’s Third Law of Motion states that for every action force, there is an equal and opposite reaction force. Forces always occur in interacting force pairs. Interacting force pairs are equal in size and opposite in direction. Is the force of the bullet forward equal to the force of the rifle backward? Are the accelerations equal? Why Yes No, the mass of the rifle is much greater than the mass of the bullet. Force is the same, so… if  Mass bullet then  Acceleration bullet if  Mass rifle then  Acceleration rifle

Interacting Force Pairs Why don’t force pairs cancel each other out? Force pairs do not act on the same object. 1st object exerts action force on 2nd object. 2nd object exerts reaction force on 1st object (equal in size, opposite in direction). Equal forces don’t always have equal effects. For example, the action force of Earth pulling on an object and causing it to fall is much more obvious than the equal and opposite reaction force of the falling object pulling on Earth.

Identifying Interacting Force Pairs Action Force = Bowling ball pushes pin left. What is the reaction force? Pin pushes bowling ball right.

Identifying Interacting Force Pairs Action Force = Enclosed air particles push balloon wall outwards. What is the reaction force? Balloon wall pushes air particles inward.

Identifying Interacting Force Pairs Identify at least six force pairs in this picture.

Moving objects have momentum. Momentum is a quantity defined as the product of the mass and velocity of an object. momentum = mass x velocity p = mv Moving objects have momentum. For a given velocity, the more mass an object has, the greater its momentum is. Likewise, the faster an object is moving, the greater its momentum is.

Force is related to change in momentum. When you force an object to change its motion, you force it to change its momentum. Momentum is conserved in collisions. The Law of Conservation of Momentum states that the total amount of momentum in an isolated system is conserved.

Momentum is transferred. When a moving object hits a second object, some or all of the momentum of the first object is transferred to the second object. Momentum can be transferred in collisions, but the total momentum before and after a collision is the same. A semi and a car collide… Which will get hit farther? If they stick together… Which direction will they move?

Newton’s Laws

EXIT TICKET: #13-16

13.“For every action force, there is a reaction force that is ___ in size and ___ in direction.” a. opposite; equal b. equal; opposite c. equal; equal d. opposite; opposite

14. If 2 spheres were pulled to the left on a Newton’s Cradle and then released, how many will move to the right? a. 1 b. 2 c. 3 d. 4

15. If the action force is a hockey stick pushing a puck to the left, then the reaction force is the ___. a. puck pulling the hockey stick to the left b. puck pulling the hockey stick to the right c. puck pushing the hockey stick to the left d. puck pushing the hockey stick to the right

16. If the action force is a bowling ball pushing a pin to the right, then the reaction force is the ___. a. pin pushing the bowling ball to the left. b. pin pushing the bowling ball to the right c. bowling ball pulling the pin to the left d. bowling ball pulling the pin to the right