Gravity & Motion Section 10.2 Standard 2: Forces d. Students know how to identify separately the two or more forces that are acting on a single static object, including gravity, elastic forces due to tension or compression in matter, and friction. 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). f. Students know the greater the mass of an object, the more force is needed to achieve the same rate of change in motion. g. Students know the role of gravity in forming and maintaining the shapes of planets, stars, and the solar system.

Law of Universal Gravitation Gravity What is gravity? Force that pulls objects towards each other Who concluded this? Sir Isaac Newton Where does gravity apply? Everywhere! Law of Universal Gravitation Gravity acts between all objects in the universe So why can you “float” on the moon? So why are we not sucked in toward each other like we are the Earth?

Mass & Distance Force of gravity between objects… Increases with greater mass Decreases with less mass Increases with closer distance Decreases with greater distance This is what keeps our planets in orbit! The mass of the sun is HUGE. So, the gravity is HUGE. Closer planets, like Mercury, are held tighter in orbit. This makes them travel very fast!

Mass vs. Weight What is weight? Gravitational force exerted on an object, directed towards Earth What is mass? A measure of how much matter is in an object How are they the same? Objects with greater mass have greater weight. How are the different? Mass never changes! It will be the same everywhere. Gravity will be different on each planet. Weight = Mass x Acceleration due to Gravity Acceleration due to Gravity = 9.8 m/s2 What is the SI Unit for Weight? Mass?

Math Practice Leroy has a mass of 60 kg and is hanging out on earth. What is Leroy’s weight? Step 1: First write the equation: Weight = Mass X Acceleration due to gravity Step 2: Fill in what you know Weight = (60 kg) X (9.8 m/s2) Step 3: Solve for the missing piece! Weight = 588 N Acceleration due to gravity on the moon is 1.6 m/s2. What is Leroy’s mass on the moon? What is Leroy’s weight on the moon?

Free Fall What is free fall? When Gravity is the ONLY force acting on object. Object accelerates (speeds up) downward Acceleration due to Gravity = 9.8 m/s2 Same for ALL objects…regardless of mass! What does that mean? Velocity increases 9.8 m/s each second it falls. After 1 second, velocity has increased to 9.8 m/s After 2 seconds, velocity has increased to 19.6 m/s After 3 seconds, velocity has increased to ________ After 4 seconds, velocity has increased to ________

Free Fall 1 4 9 16

Textbook page 386 “Math Analyzing Data” Answer questions #1-4. Math Practice

Air Resistance If everything falls at the same rate, why does it take longer for a leaf or piece of paper to reach the ground than a ball? Fluid Friction acts in OPPOSITE direction to motion. Fluid  Air! . . . so we call it air resistance Upward force exerted on falling objects Which object will experience greater air resistance? An object with a large surface area or a small surface area? Can you think of an example? Greater Surface Area = Greater Air Resistance

This man made history this weekend! Do you know how? Let’s look at it! http://www.usatoday.com/story/news/nation/2012/10/14/skydiver-sound-barrier-baumgartner/1632329/ In free fall, an object gains speed each second it is falling. This man, fell from over 24 miles above Earth’s surface! He reached a top speed of Mach 1.24 / 833.9 mph / 372.8 m/s He was falling for just over 9 minutes! Only half of that was in free fall because he reached “terminal velocity” Terminal velocity means air resistance = gravity What happens when forces are balanced? What was his average speed?

Projectile Motion What is a projectile? An object that is thrown Once released, the only force acting on it is gravity. Isn’t this the same as free fall? Gravity will act on an object in free fall and a projectile at the same rate. They will hit the ground at the same time. Despite mass and being thrown horizontally!

Recap Gravity Weight = Mass X Acceleration due to Gravity Mass vs. Weight Mass is a unchanging property or measurement of “how much” Weight is a force! It will change on different planets Free Fall Objects in free fall experience only 1 force: gravity On Earth, objects gain 9.81 m/s in speed each second falling Air Resistance Air resistance is a form of fluid friction. Greater Surface Area = Greater Air Resistance Projectiles Gravity is all that acts on projectiles.