Air Resistance Free Fall Motion and Falling Objects

Air Resistance, Free Fall Motion and Falling Objects Chapter 3. 3

Lesson-Specific Learning Targets (10/20) I can identify the composition of the Earth’s atmosphere p I can define air resistance and why it is a force p I can define terminal velocity p

Air Resistance Starter Q (10/20) Provide answers to these three questions: (see handout)

Starter Q (10/24) Provide answers to these three questions: 1. Describe the Earth’s atmosphere. (What is it and what is it made of? ) p 2. Describe air resistance (what causes it and why is it considered a force? ) p 3. Describe the term aerodynamic shape. (What does it mean? Give an example) p

Starter Q (10/20) 2. Describe air resistance (what causes it and why is it considered a force? )

Starter Q (10/20) p 3. Describe the term aerodynamic shape. (What does it mean? Give an example)

Earth’s Atmosphere Major Constituents • Nitrogen (N 2) 78% • Oxygen (O 2) 21% • Argon (Ar) < 1% Minor Constituents Water vapor (H 2 O) Carbon dioxide (CO 2) Methane (CH 4) Nitrous oxide (N 2 O)

AIR RESISTANCE A resistance force caused by air molecules opposing the motion of an object as it moves through the air. p A form of friction sometimes called drag. p Aerodynamic shape

Lesson-Specific Learning Targets(10/21) p p I can explain two factors that determine the air resistance acting on any falling object I can determine what changes applied to a falling object would increase the air resistance force and I can give examples. I can explain the relationship between an object’s weight and gravitational force acting on the object. I can explain how the velocity and acceleration change for an objects as it falls

Starter Q (10/21) Air resistance Quick response: how do these pictures relate to the study of air resistance?

Suppose a bowling ball is falling… p How many forces are acting on it? 2 Air Resistance Force Gravitational force The weight of the bowling ball is the same as the gravitational force acting on the ball (reported in Newtons)

Homework

Interpreting Motion Graphs The velocity-time graph is useful for determining whether a falling object is accelerating or at a constant velocity (terminal velocity) p Interpret the graph given to you. p

Questions p Does every object fall the same? Why or why not? p What happens to the air resistance when an object ‘s exposed surface area increases? Decreases? p Does air resistance increase, decrease or stay the same when an object travels faster through the air?

Free Fall An object moving only under the influence of the gravitational force is in free fall. The acceleration of an object in free fall on Earth is 9. 8 m/s 2. For free fall, neglect air resistance!

Free Fall Free body diagram p Only under the influence of gravitational force. No air resistance force! Rock that weighs 100 N This object will continue to gain speed at a rate of 9. 8 m/s 2. Fgrav = 100 N

Free Fall: How Fast During each second of fall the speed of by the object increases by an additional 9. 8 meters per second. This gain in speed per second is the acceleration. After 1 second = 9. 8 m/s After 2 seconds = 9. 8 m/s x 2 After 3 seconds = 9. 8 m/s x 3… and so on

Free Fall: How Fast 9. 8 m/s 19. 6 m/s 29. 4 m/s 39. 2 m/s 49 m/s 9. 8 m/s x t

Free Fall: How Fast Rising Objects Rising objects decelerate at the same rate that falling objects accelerate. During the upward part of this motion, the object slows from its initial upward velocity to zero velocity. The object decreases in speed at the same rate that it increases in speed as it rises and falls

Air Resistance and Falling Objects Drop a feather and a hammer on earth and the hammer reaches the floor far ahead of the feather. What about on the Moon? http: //history. nasa. gov/40 thann/videos. htm

Earth vs. Moon Contrast These Characteristics of the Earth and Moon Magnetic field Atmosphere Gravity Density Radius Surface Plate Tectonics Water Cycle Rock Cycle Earth Moon

Air Resistance and Falling Objects A feather and a coin accelerate equally when there is no air around them. Vacuum tube

Air Resistance and Falling Objects How objects fall without air resistance? F gravity or weight is the only force

Air Resistance and Falling Objects How objects fall without air resistance? Objects accelerate equally. F gravity or weight is the only force

Free Fall p Physicists consider air resistance to be negligible for heavier objects that fall near the surface of the Earth. Fg = 71. 2 N Fg = 100 N Don’t worry about air when making calculations! Fg = 11 N

Falling and Air Resistance Air resistance does not depend upon the weight of the object. The amount of air resistance force an object experiences depends on the object’s speed and exposed surface area. 1. Speed The greater the speed, the greater the air resistance. 2. Surface Area (exposed or frontal) The greater the surface area, the greater the air resistance.

Falling and Air Resistance What two factors determine the air resistance force on an object? The speed and the exposed surface area

1. The Moon formed out of the Earth p Scientists now think that the Moon was formed when a Mars-sized object crashed into our planet about 4. 5 billion years ago. The collision was so large that a huge spray of material was ejected into space. The orbiting ring of debris gathered itself into a sphere, and formed the Moon. How do we know that this is how the Moon probably formed? The Moon seems to be much less dense than the Earth and lacks a lot of iron in its core. Scientists think that the Moon is made up of the upper crust material, which has mostly lower density, than the composition of the Earth.

p p 2. The Moon only shows one face to the Earth Although the Moon used to rotate in the sky compared to our point of view, it has been slowing down billions of years. And at some point in the distant past it just stopped turning from our perspective. The Earth’s gravity holds the Moon in orbit, but it pulls differently at various parts of the Moon. Over a long period, gravity slowed down the Moon’s rotation so that it finally stopped, and always displayed one face to the Earth. A similar situation has happened with most of the large moons in the Solar System. In fact, in the case of Pluto and Charon, but objects are tidally locked to each other, so they present only one face to the other.

p p 3. The Moon is slowly drifting away Although the orbit of the Moon seems nice and stable, our only natural satellite is actually drifting away from us at a rate of 4 centimeters a year. This is happening because of the conservation of momentum in the orbit of the Earth. In about 50 billion years from now, the Moon will stop moving away from us. It will settle into a stable orbit, taking about 47 days to go around the Earth (it takes 27. 3 days today). At that point, the Earth and the Moon will be tidally locked to each other. It will look like the Moon is always in the same spot in the sky. Of course, the Sun is expected to consume the Earth in about 5 billion years, so this event may not happen.

p p 4. The Moon looks the same size as the Sun This is an amazing coincidence. From our perspective here on Earth, but the Moon and the Sun look approximately the same size in the sky. Of course, the Sun is much bigger than the Moon. The Sun happens to be 400 times larger than the Moon, but it’s also 400 times further away. This wasn’t always the case. Billions of years ago, the Moon was much closer than the Sun, and would have looked larger in the sky. And the Moon is moving away from us, so in the distant future, the Moon will look much smaller than the Sun.

p p 5. The Moon causes most of the tides… but not all You might know that the tides on Earth are caused by the gravitational pull of the Moon. But it’s not the only thing pulling at the Earth’s water, the Sun is helping out too. This is why we get very high and low tides from time to time. When the gravity of the Moon and the Sun line up, we get the biggest and smallest tides. Did you know that the Moon is also pulling at the crust of the Earth causing it to bulge up? You actually move a few meters every time the Moon is overhead, but you just don’t notice.

p 6. Gravity on the Moon is only 17% of the Earth p Want an easy way to lose some weight? Take a trip to the Moon and stand on its surface. Since the pull of gravity on the Moon is only 17% the pull of gravity on the Earth, you’ll feel much lighter. Just imagine, if you weighed 100 kg on the Earth, you would feel like you only weighed 17 kg on Earth. You would be able to jump 6 times further and carry objects 6 times as heavy. In fact, you had wings attached to your arms, you could even fly around inside a dome on the Moon under just your own muscle power.

p 7. The official name for the Moon is… the Moon p I know it’s kind of confusing, but the only real name for the Earth’s Moon is “the Moon”. When the Moon was given its name, astronomers didn’t know that there were moons orbiting other planets. And so they just called it the Moon. Now that we know there are other moons, it all comes down to the capitalization. The Earth’s moon is referred as “the Moon”, with a capital “M”. Other moons are given a lowercase “m” to show the difference.

8. The Moon is the 5 th largest natural satellite in the Solar System p You might think that the Moon is the largest satellite in the Solar System. I mean look at it, it’s huge! But there actually larger moons in the Solar System. The largest moon is Jupiter’s Ganymede (5, 262 km), followed by Saturn’s Titan, Jupiter’s Callisto, Jupiter’s Io, and finally, the Earth’s Moon with a mean diameter of 3475 km. p

Only 12 people have ever stepped onto the surface of the Moon p Only a tiny group of astronauts have ever set foot on the surface of the Moon. These were the astronauts on board the Apollo missions going from 1969 to 1972. The first person to ever walk on the Moon was Neil Armstrong. And the last person on the Moon was Gene Cernan, who followed his partner Jack Schmitt into the lunar lander on December 14, 1972. p

Lesson-Specific Learning Targets p p p p I can explain how the velocity and acceleration change for an objects as it falls from a tall building I can explain two factors that determine the air resistance acting on any falling object I can determine what changes applied to a falling object would increase the air resistance force and I can give examples. I can draw free-body diagrams showing how the weight (gravitational force) of an object is influenced by air resistance. I can determine how objects of different masses and shapes would fall without air resistance on Earth. I can identify that an object’s weight equals the gravitational forces acting on the object. I can identify the rate of acceleration due to gravity on Earth I can identify that in the absence of air resistance, all objects regardless of size, shape or mass will fall at the same rate. I can explain key differences between the Moon and the Earth that influence how objects fall. I can explain why a feather and a hammer fall differently on the Moon than on the Earth I can explain why falling objects reach terminal velocity. I can determine why objects could never reach terminal velocity. I can analyze motion graphs to identify when objects are accelerating and when they reach terminal velocity.