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Earth’s Forces

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Chapter 14

Earth’s Forces

- Watch your teacher perform the Egg Drop demonstration.
- Predict: What will happen to the egg if a force caused the pan to suddenly move?
- Think about this:
- What forces are acting on the objects before, during, and after the demonstration.
- What happened to the egg and why do you think this was the outcome?

- A force is a push or pull; things move when they are acted on by a force.
- Often, more than one force acts on an object at the same time. The total of all the force on the object is called the net force.
- When forces act against each other with equal strength in opposite directions, the net force is ZERO and the object will not move.
- When one force is greater than the other the net force is NOT ZERO and the object will move.

F = 20 N

East

F = 20 N

West

F = 18 N

East

F = 20 N

West

- In science, any change in an object’s motion is called acceleration.
- Refers to an object’s
- Increasing speed
- Decreasing speed
- Changing direction
- Changing speed and direction

- Sir Isaac Newton was an English scientist in the late 1600’s who proposed three laws of motion.
- Newton’s three laws of motion explain how inertia, an object’s mass, acceleration, and the forces acting on the object are related.

- Objects at rest will remain at rest unless acted on by a nonzero net force.
- Objects moving at a constant speed and direction (velocity) will continue moving at that rate unless a nonzero acts on it.
- The tendency of an object to resist a change in motion is called inertia.
- http://teachertech.rice.edu/Participants/louviere/Newton/law1.html

- If you kick a soccer ball, and no one stops it, why does it eventually slow and stop?
- Friction and gravity are forces that act against it

- How can I make the soccer ball go further?
- Reduce the friction (on concrete or ice vs grass) or increase the force that you kick with (kick it harder)

- If I roll a soccer ball and a bowling ball with the same force on the street, which one would be harder to stop?
- The bowling ball because it has more mass and it’s inertia is greater

- Think about what happens to the pipes when you drop the cup. What causes this to occur?
- Try This: Put the penny on your elbow then try to catch the penny with the same hand. How is this possible? Can you explained this using Newton’s 1st Law of Motion?

- An object’s acceleration depends on its mass (the amount of matter in an object) and the net force acting on it.
- The mathematical equation for this law is:
- Force (F) = Mass (M) x Acceleration (A)
Or:

- Acceleration (A) = Force (F) / Mass (M)

- Force (F) = Mass (M) x Acceleration (A)
- http://teachertech.rice.edu/Participants/louviere/Newton/law2.html

- On a swing, who would require more force to push? Why?
Jonathan Vilma: or Steve Urkel

6’11” / 230 lbs5’6” / 110 lbs

- On a swing, if you applied the same force to each person, who would have the greatest acceleration? Why?
- Jonathan Vilma: or Steve Urkel
- 6’11” / 230 lbs5’6” / 110 lbs

- Using your left pinky finger, try to push the paperback book across the table.
- Using the same finger, try to push the hardback book across the table.
- Which required more force? Why?
- Can you explain this using Newton’s 2nd Law of Motion?

- If one object exerts a force on another object, then the second objects exerts a force of equal strength in the opposite direction.
- “For every action there is an equal and opposite reaction.”
- http://teachertech.rice.edu/Participants/louviere/Newton/law3.html

- What happens when you blow up a balloon, then let it go (without tying then open end)?
- Why does this happen (using Newton’s 3rd Law of Motion)?

- Watch what happens when you drop the basketball and tennis balls separately.
- Watch what happens when you drop the basketball and tennis balls together.
- What’s the difference between the two drops?
- Why do you think this happened? Explain this using Newton’s 3rd Law of Motion.

- Make a fork and spoon magically “levitate” on the glass using the provided materials.
- Think about this: Which of Newton’s Laws are you using to complete this “magic trick”?

- The force that pulls an apple to the ground also pulls satellites (including the moon and International Space Station) toward Earth, keeping them in orbit.
- Gravity attracts all objects toward one another.
- Newton’s Law of Universal Gravitation states that every object in the universe attracts every other object.

- The strength of the force of gravity between two objects depends on two factors:
- The mass of the objects
- The distance between the objects

- Mass is the amount of matter in an object
- Earth is extremely massive and therefore exerts more force than you

- The force of gravity decreases as the distance increases
- The further an object, the less gravity is exerted on the object

- The measure of the force of gravity on an object is called weight.
- If you go to the moon, what would change, your mass or your weight?
- Your WEIGHT would change depending on your location (like the moon) because the gravity is different there (1/6th as much)

- Why is gravity different on the moon than on Earth?
- The moon has less mass than Earth, so it also has less gravitational pull.

- Recall Newton’s 3 Laws of Motion and think about which one may explain this:
- What keeps objects orbiting Earth (like the moon, satellites, or the International Space Station)?

- Newton concluded that inertia (1st Law of Motion) and gravity keep Erath in orbit around the sun, and the moon and ISS in orbit around Earth.

- You will be working on a group project creating a game that can be played on the International Space Station.
- To do this, you will be putting to use the information we learned about forces, Newton’s Laws of Motion, and gravity.

- How are things different in space than they are here?
- How do objects move differently in space?
- If I hit an object in space, with micro-gravity, what would happen to that object?