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Title: Newton's Laws of Motion Discrepant Events
Principle(s) Investigated: Acceleration due to gravity, air resistance, unbalanced forces, balanced forces, inertia, and Newton's three laws.
Standards : Forces
2. Unbalanced forces cause changes in velocity. As a basis for understanding this concept:
a. Students know a force has both direction and magnitude.
b. Students know when an object is subject to two or more forces at once, the result is the cumulative effect of all the forces.
c. Students know when the forces on an object are balanced, the motion of the object does not change.
e. Students know that when the forces on an object are unbalanced, the object will change its velocity (that is, it will speed up, slow down, or change direction).
Materials: A textbook, a sheet of paper, several eggs, three toilet paper rolls (without toilet paper), three cups or glasses of equal size, a pie tin, water, and a blanket. All of these items can be found around your house, your school, or easily acquired at any store.
Procedure:
Egg Drop Trick- Newton's Law of Inertia
Warning: Always wash your hands well with soap and water after handling raw eggs. Some raw eggs contain salmonella bacteria that can make you really sick!
- Fill the large drinking glass about three-quarters full with water.
- Center a pie pan on top of the glass.
- Place the cardboard tube on the pie plate, positioning it directly over the water.
- Carefully set the egg on top of the cardboard tube.
- With your writing hand, smack the edge of the pie pan horizontally. Don't swing up, and don't swing down! It’s important that you hit the pie pan horizontally and use a pretty solid hit, so plan on chasing the plate and tube.
- Your astonished guests will watch the egg plop nicely into the water. It’s even more fun to watch someone else try to drop the egg. Science is so cool!
Take It Further!
Take It Further!
- Try setting up a tray (like one that you would get from a fast food restaurant) on top of five glasses. USe five tubes and five eggs and see if you are an egg drop master! *HINT* The angle that you hit the tray from can make all the difference.
- Add coloring to the water in your egg drop for added effect.
- Try testing longer tubes, more or less water, different liquids in the glass, different water containers, and heavier or lighter falling objects.
Student prior knowledge: Newton's Laws of Motion, mass, gravity and other forces.
Explanation:
Newton's First Law
Newton's First Law
Newton's first law of motion is often stated as
An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.
State of Motion
State of Motion
Inertia is the tendency of an object to resist changes in its state of motion. The Latin root for inertia is the same root for "inert," which means lacking the ability to move. But what is meant by the phrase state of motion? The state of motion of an object is defined by its velocity - the speed with a direction. Thus, inertia could be redefined as follows:
Inertia: tendency of an object to resist changes in its velocity
An object at rest has zero velocity - and (in the absence of an unbalanced force) will remain with a zero velocity. Such an object will not change its state of motion (i.e., velocity) unless acted upon by an unbalanced force. An object in motion with a velocity of 2 m/s, East will (in the absence of an unbalanced force) remain in motion with a velocity of 2 m/s, East. Such an object will not change its state of motion (i.e., velocity) unless acted upon by an unbalanced force. Objects resist changes in their velocity.
An object that is not changing its velocity is said to have an acceleration of 0 m/s/s. Thus, we could provide an alternative means of defining inertia:
Inertia: tendency of an object to resist accelerations.
May the Force Be with You
The F, the m and the a in Newton's formula are very important concepts in mechanics. The F is force, a push or pull exerted on an object. The m is mass, a measure of how much matter is in an object. And the a is acceleration, which describes how an object's velocity changes over time.Velocity, which is similar to speed, is the distance an object travels in a certain amount of time.
Mass Matters
Mass plays a part in the experiment because the more eggs you put on the tray, the more total mass that is on top of the tray. Relating this to the above example, if you push an elephant and a mouse with the same force each time, the mouse ends up with a larger velocity than the elephant because it has a smaller mass. And if you try to stop an elephant and a mouse that are already traveling with the same velocity, you’ll get flattened by the elephant if you push it with the same force that you need to stop the mouse. The more massive something is, the greater its inertia, or tendency to continue with its current velocity, and the larger the force you have to push it with to produce the same change in velocity.
Sources: The Physics Classroom, How Stuff Works, and Head First Physics
Questions & Answers:
1. Why is Newton's First Law hard to observe on Earth?
ANSWER:There is always the unseen force of friction at work. In order for an object to remain in motion, Newton's first law clearly states that no force can be acting against the object in motion. Newton's first law would be better observed in a vacuum like space because there is no air resistance (no friction).
2. Imagine a place in the cosmos far from all gravitational and frictional influences. Suppose that you visit that place and throw a rock. Explain what the path of the rock would look like.
ANSWER: According to Newton's first law of motion the rock will continue in the same path and the same speed forever, or until an unbalanced force acts on it.
3. Supposing you were in space in a weightless environment, why would it be harder to move an object in space than on earth (assume the item has the same mass).
ANSWER: The inertia of the object is the same, but there would be no friction. When you push the object, it will push back sending you backward into space. An example on earth would be to try to push a heavy door open while wearing roller skates.
Applications to Everyday Life:
1. You throw a rock and it hits the ground.
Inertia keeps the baseball in your hand until an unbalanced force acts on the ball. The force is provided by the person throwing the ball. Inertia staes that the ball wants to remain in motion, but the force of gravity prevents that from happening. When the ball eventually hits the ground, the ground provides another force that cause the ball to stop (change of motion). Inertia states that the ball will remain on the ground until another unbalanced force acts on the ball.
2. Traveling in a car and hitting the brakes.
While traveling in car, you are traveling at the same speed as the car. When you apply the brakes, the car slows down but the passengers inside want to keep going the same speed (inertia). The person or animal in the car will either be stopped by their seatbelt or the object in front of them.
3. Two people push equally hard on opposite sides of a large couch and the couch doesn’t go anywhere.
A couch has inertia because it has mass. It will remain at rest until an unbalanced force acts on it. Even though there are two forces acting on the couch, they are equal forces and in opposite directions. The net force of the two forces is 0 Newtons (0 N), producing a balanced force, or no movement.
Source: Stop Faking It! Finally Understanding Science So You Can Teach It: Forces and Motion
Photographs:
The setup: three cups under a pie tin with three hollow tubes placed over the center of each cup. The eggs are placed sideways .
So the initial run does not not goes as planned....
My wife tells me I need to not be so messy, so I improvise.
SUCCESS!!!
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