CHAPTER 3 SECTION 1: GRAVITY, FRICTION, AND PRESSURE
Big Idea: Newton’s laws apply to all forces.
Key Concept: Gravity is a force exerted by masses.
Now we will learn:
· How mass and distance affect gravity.
· What keeps objects in orbit.
· The force that objects exert on each other because of their masses.
· Gravity is not only present on Earth.
· Considered a universal force.
II. The Force of Gravity
· If there is a force between all masses, why are you not pulled toward your desk by the desk’s gravity? (See page 78 of book)
· Strength of gravity depends on:
· The more mass two objects have, the greater the force of gravity.
· As distance increases, gravity between objects decreases.
III. Gravity on Earth
· Acceleration due to Earth’s gravity is called g.
· 9.8 m/s/s
· Calculate the force of gravity: F=ma or F=mg
IV. Weight and Mass
· Weight is the force of gravity on an object.
· You have the same mass no matter where you are.
· Weight can change depending on where you are.
· How much would you weigh on the moon? Multiply your weight by .17 to find out!
V. Gravity keeps objects in orbit
· An orbit is an elliptical path one body follows around another body due to the influence of gravity.
Read bottom of page 80
VI. Spacecrafts and people in orbit
· In order to send an object into orbit it needs to accelerate to 8000 m/s to match the curve of the earth’s surface.
· Escape velocity: 11000 m/s
· How do you feel when you are riding down in an elevator? Read page 80.