write the third law of motion in detail with full example
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Answer:
Examples of Newton's third law of motion are ubiquitous in everyday life. For example, when you jump, your legs apply a force to the ground, and the ground applies and equal and opposite reaction force that propels you into the air. Engineers apply Newton's third law when designing rockets and other projectile devices.
Answer:
Be ready to show students the Forces and Newton's Third Law Presentation (a seven-slide PowerPoint® presentation) to teach the lesson.
For the Hero's Engine demonstration, have handy a soda can, nail, piece of string and water. Use a nail to poke four holes around the base of an empty soda can. When the nail is in each hole, push the nail to the left or the right to angle the hole so the water will stream out on a tangent to produce thrust; do the same for each hole. Tie a string to the tab. For the demonstration, fill the can with water and lift it with the string over a sink or tub (or outside) so students can observe the rotational movement of the can spinning as water flows out of the holes. Refer to slide 2 and NASA Pop Can "Hero Engine" for instructions.
In advance, make copies of Newton's Final Quiz (one per student).
At some point during the presentation, perhaps when talking about some action-reaction examples (slides 3-6), go over how to draw the (conceptual) free-body diagram vectors (arrows) of force, velocity and acceleration, which students will be asked to do as part of the homework assignment.
Newton's Third Law of Motion Presentation Outline (slides 1-7)
Open the Forces and Newton's Third Law Presentation for all students to view and present the lesson content, guided by the script below and text in the slide notes. The slides are animated so clicking brings up the next text/image/answer.
Objective: To be able to identify action-reaction force pairs.
(slide 2) Introduce Newton's third law of motion: for every action, there is an equal and opposite reaction. Ask students: Have you heard this before? What do you think it means?
Then demonstrate the third law by showing students a modern version of Hero's Engine, which takes just a few minutes. Hero of Alexandria was an ancient Greek mathematician and experimentalist who lived in Egypt. His original engine was steam-powered, but the soda can version works well to demonstrate the same concept. For the demo, fill the prepared can with water and lift it with the string over a sink or tub (or outside) so students can observe the rotational movement as water flows out of the holes and the can spins. The can spins due to the reaction force associated with the flow of water.
Alternatively, demonstrate the third law by having one student sit on a scooter with a basketball and then throw the ball to another student. The reaction force from the throw is evident when the throwing student is propelled backward on the scooter.
(slide 3) Tell students that forces come in what are called "action-reaction force pairs." This slide shows a stack of concrete blocks resting on the ground. Identify the action-reaction pair for the class: the block's weight pushes on the ground and the ground pushes back up on the block.
(slide 4) Next, ask students to identify the action-reaction pair in the photograph of a firing cannon. The cannon exerts a force on the cannon ball, and the cannon ball exerts an equal and opposite force on the cannon. Point out that Newton's third law explains the recoil of projectile weapons such as cannons and guns. Students who have seen Wall-E may recall a scene in which the robot uses the fire extinguisher as a propulsion system (the reaction force causes the robot to move). Another good third law/recoil example is a garden hose dancing around the yard, moving because of the force of water running through it.
(slide 5) Ask students to identify the action-reaction force pairs in the photograph of a space shuttle launch. The space shuttle exerts a downward force, and the reaction force pushes it upwards.
(slide 6) Challenge students to identify all the action-reaction force pairs in this photograph of two football players. Examples: hand-helmet, hand-shoulder, ball-hand, shoe-ground.
This may be a good time to review how to draw (conceptual) free-body diagram vectors (arrows) of force, velocity and acceleration.
(slide 7) Review the concepts from all three lessons in this unit. Conclude the presentation with a review of the key concepts, as listed on the slide, with blanks for students to supply the answers. Through these three lessons, expect students to have developed an understanding of Isaac Newton's three laws of motion. These fundamental laws of physics describe how forces impact the motion of objects. Without forces, no changes in motion can occur. Understanding forces can be a very powerful thing! Because engineers understand how forces cause objects to slow down, speed up and turn, they are able to design complicated mechanical systems ranging from airplanes to door knobs to delicate drug delivery systems.
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