Newton's Third Law (Arbella Moshava)
Title: Newton’s third law
Principle(s) Investigated:
· Students will understand the Newton’s third, for each reaction there is an equal and opposite reaction
· Students will understand the relationship between forces and the motion.
Materials:
· 2 cans
· a 40-50 centimeter length of string
· 1small nail
· 1large nail
Procedure:
- Lay the can on its side and use the nail to punch a single hole near its bottom. Before removing the nail, push the nail to one side to bend the metal, making the hole slant in that direction.
- Bend the can’s opener lever straight up and tie a 40-50 centimeter length of string to it.
- Submerge the can in the container and fill the can to the top with water.
- Quickly lift the can with the string so that it is 1-2 cm above the water level in the container.
- Count how many spins the can completes in 10 seconds. Record the results
- Add a 2nd hole on the opposite side of the can and repeat.
- Try the activity with another soda can using a larger nail.
Student prior knowledge:
Students need to know the concept of Newton’s third, second, and first law. The Newton’s first law states that the motion of an object will change only if unbalanced forces act on the objects. The Newton’s second law of motion states that the acceleration of an object depends on the object’s mass and on the force exerted on the objet. The Newton’s third law of motion states that whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first.
Explanation:
Action and Reaction: Newton’s 3rd Law, for every action, there is an equal and opposite reaction.
Newton’s third law of motion stated that whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first.
A force is always applied by one object on another object. This rule is true for all forces, including action hand reaction forces. However, action and reaction forces in a pair don not act on the same object. If they did, the net force would always be o N. So, nothing would ever move. The action force is applied to the water by the swimmer’s hands. But the reaction force is applied to the swimmer’s hands by the water. The forces do not act on the same object. The action force and reaction force are a pair. The two forces are equal in size but opposite in direction.
Run to the right, canoe moves to the left
Questions & Answers:
1) What was the action? What was the reaction?
The action was water flowing out and the reaction was spinning of the can in opposite direction.
2) How would adding more holes affect the spinning of the can?
By adding more holes, the spinning of the can will increase. The reason is because for every action (flowing out water), there is an equal and opposite reaction (spinning of the can).
3) What would happen if you punch a hole near can’s bottomed and bend it to the right and the other hole bend it to the left?
The can will not move because forces form water shooting out will equalize.
Applications to Everyday Life:
· The space shuttle’s thrusters push the exhaust gases down-ward as the gases push the shuttle upward with an equal force.
· Gravity is a force of attraction between objects that is due to their masses. If you drop a ball, gravity pulls the ball toward Earth. This force is the action force exerted by Earth on the ball. But gravity also pulls earth toward the ball. The force is the reaction force exerted by the ball on Earth.
· The rabbit’s legs exert a force on the ground. The ground exerts an equal force on the rabbit’s legs and causes the rabbit to accelerate upward.
Videos:
http://www.youtube.com/watch?v=6s2V2yoBpwA
Sources:
http://www-istp.gsfc.nasa.gov/stargaze/Snewton3.htm