Chapter 6 Forces and Motion Section 1 Gravity and Motion

Essential Questions for 6-1 What are the effects of gravity and air resistance on falling objects? Why are objects in orbit in free fall? Why do they appear to be weightless? How is projectile motion affected by gravity?

Gravity and Falling Objects Objects fall to ground at the same rate because acceleration due to gravity is the same for ALL objects Why? Acceleration depends on both force and mass. A heavier object experiences a greater gravitational force, BUT it is also harder to accelerate. Galileo was a genius.

Acceleration and Velocity Acceleration is the rate velocity changes over time. The acceleration of an object affected by gravity is 9.8 m/s. Change in velocity of falling objects can be measured by the following equation: ∆v = g x t OR 9.8 m/s times the number of seconds an object falls…

Air Resistance Air resistance – the force that opposes the motion of objects through air Amount of air resistance depends on the size, shape, and speed of the object

Discussion Why would a feather dropped from the same height as an acorn fall to Earth more slowly than the acorn?

Discussion How can a sky diver benefit from air resistance?

Terminal Velocity Terminal Velocity – when air resistance = gravity 0 N or a balanced force! It’s the fastest an object will fall It’s also why rain drops don’t kill you… think about it…

Free Fall Free fall - when gravity is the only force acting upon an object Can only happen where there is NO air resistance: SPACE (or a vacuum) - Orbiting objects are in free fall. Orbit is caused by two motions: - Orbiting objects move forward, but are also in free fall – so are the astronauts

Discussion How does free fall in an orbiting spacecraft cause the appearance of weightlessness?

Orbiting and Centripetal Force Orbit is caused by two things that create an unbalanced force Gravity provides centripetal force to the orbiting object Centripetal force – the unbalanced force that causes an object to move in a circular path Ex: planets around the sun or the moon around the Earth

Discussion What does free fall in an orbit look like? Which is The path of the orbiting spacecraft? The path of free fall for the spacecraft? The path the spacecraft would follow if there was no gravity? The curve of the Earth’s surface?

Projectile Motion The curved path an object follows when it is thrown near the surface of the Earth Composed of horizontal motion and vertical motion Horizontal motion (like throwing a ball) causes the object to go forward Vertical motion (gravity) causes the object to fall Together they create a curved path: BUT still hits the ground the same time as a dropped object This is why you always have to aim above a target when trying to hit it…

An example of projectile motion

Quiz 6-1: 4 Questions 1. If a baseball and a cannonball are dropped from the same height at the same time, and there is no air resistance, which ball will hit the ground first? a. The cannonball lands first. b. The baseball lands first. c. The balls land at the same time. d. The ball with the larger volume lands first.

2. What feature of an object does not affect air resistance. a 2. What feature of an object does not affect air resistance? a. its size b. its chemical properties c. its shape d. its speed

3. Why do astronauts in space appear weightless? There is no gravity in space. b. Air resistance opposes gravity. c. They have no mass in space. d. They are in free fall.

4. In what directions is a projectile accelerated. a 4. In what directions is a projectile accelerated? a. both vertically and horizontally b. vertically downward c. vertically upward d. horizontally forward