Newton’s 3rd

Remember the balloon rockets? What two things were acting in this system? balloon and air Which way did the air push on the balloon? air pushed the balloon forward Which way did the balloon push on the air? balloon squeezed the air out backward

Newton had a law for this… Newton’s 3rd Law says: Whenever Thing 1 pushes on Thing 2, Thing 2 pushes back on Thing 1 in the opposite direction with the same force Write this down!

Take notice: (write these down) There are always 2 objects in a SYSTEM of forces (not the same as tug-o-war forces on the same rope.) The opposing forces always come in pairs. (Sometimes called an action-reaction pair) Even though the forces are equal, if the MASSES of the objects are not the same, one will move and the other will not. (Remember F= ma?)

Click on the picture to launch the video A video explanation… Click on the picture to launch the video

Newton on the International Space Station Click on the picture to get a good visual explanation of Newton’s 3rd law.

https://www.youtube.com/watch?v=GPnLShiJ-t4

Now test your understanding… For each scenario Make a quick sketch in your notebook Label the two objects in the system (just pick two if there are more than two) Draw arrows and label the name of the force in each direction Indicate which direction an object will move if the objects have different mass If objects have similar mass (or very little friction) indicate the directions of motion for both objects

Getting off of a Boat Take 1 minute to: *sketch a quick model *label the 2 things interacting in the system *draw arrows representing the forces *describe which direction thing 1 and thing 2 will move

Person-Boat System Model Collision System: Body and Boat motion motion Body pushes against boat and boat moves backward Boat pushes against body and body moves forward.

At the Ice Rink Take 1 minute to: *sketch a quick model *label the 2 things interacting in the system *draw arrows representing the forces *describe which direction thing 1 and thing 2 will move

Skater-Skater System Model Collision system = skater-skater motion motion Small skater’s hands push against large skater. Large skater does not move very much. Large skater’s hands push against small skater. Small skater moves backward because the small skater has much less mass.

Newton and Serena Take 1 minute to: *sketch a quick model *label the 2 things interacting in the system *draw arrows representing the forces *describe which direction thing 1 and thing 2 will move

Tennis Racket-Ball System Model Collision system = racket-ball The racket pushes on the ball and makes the ball move a lot since it is much smaller than the racket+Serena. The ball pushes on the racket and makes the racket move backward just a little. motion motion

Lean on Me Take 1 minute to: *sketch a quick model *label the 2 things interacting in the system *draw arrows representing the forces *describe which direction thing 1 and thing 2 will move

Body-Wall System Model Since there was no motion to start with (the girl was just chillin’) and the forces are balanced, there will be no ending motion either. The body pushes on the wall, but the wall does not move The wall pushes on the body, but the body does not move.

What evidence is there that the nail is pushing back on the hammer? The hammer bounces back upward after hitting Why does the nail move LOTS more than the hammer? The hammer has much more mass than the nail, so the nail moves Hitting a Nail Click on the picture to launch the video

Football There are two pairs of action/reaction systems, can you identify them? Foot-ground Arm-shoulder pads

https://www.youtube.com/watch?v=gshAI5CkvIY

https://www.youtube.com/watch?v=EgqcGrB3re8

Exit Ticket: Draw a model that shows the action-reaction system of a person kicking a soccer ball.