CHAPTER 12 NOTES 12-1 GRAVITY

*NEWTON’S LAWS APPLY TO ALL FORCES. GRAVITY IS A FORCE EXERTED BY MASSES.

WHAT IS GRAVITY? Gravity is the word we use to describe the pull between masses. Things with more MASS produce a greater Gravity pull on each other.

MASSES ATTRACT EACH OTHER. Definition Characteristics Characteristics Examples Non-Examples Non-Examples Gravity

*GRAVITY CONTROLS…. A roller coaster’s ride A diver’s dive A skier’s jump A baseball’s fall

GRAVITY- DOWNWARD PULL (FORCE) ON OBJECTS EXERTED BETWEEN MASSES Characteristic- universal force; between masses Example: pull between the sun and the moon Non-Example: object floating in space

*FORCE OF GRAVITY Strength of gravitational force depends on mass and distance The more mass, the greater the force of gravity The greater distance between objects, the less the force of gravity

*GRAVITY ON EARTH The force of gravity acts on objects equally. Newton’s Third Law!!!! Gravity can be calculated on Earth for objects by using F=mg so W=mg instead of F=ma! Remember: g=9.8m/s 2

MASS VS. WEIGHT Do things that have more mass always weigh more?

When you stand on a bathroom scale, the scale is made of springs. The farther down you push the springs, the higher the number on the scale. The number tells you your weight. On earth it is true that the more mass you have, the more weight you have.

WEIGHT AND MASS Definition Characteristics Characteristics Examples Non-Examples Non-Examples Weight

*WEIGHT- FORCE OF GRAVITY ON AN OBJECT Depends on the force acting on the object Using a spring scale measures the pull of gravity-WEIGHT When you balance, you are measuring MASS The moon is less massive than Earth

WHAT WORD DESCRIBES HOW MUCH OF YOU THERE IS?

MASS Your mass is the amount of material that your body contains. How can you gain mass? I’d eat a looott of yummy bread to gain mass!

DOES SOMETHING THAT IS BIGGER ALWAYS HAVE MORE MASS?

DOES BIGGER= MORE MASS?

SO, HAVING MORE MASS DOES NOT MEAN TAKING UP MORE SPACE!

*THREE PROPERTIES OF MASS Has the same mass no matter where it is located Measure of how much matter an object contains A triple beam BALANCE measures mass

Weight? Mass? I am totally confused!

PRETEND THAT YOU ARE IN SPACE! You are floating around. You drift over to a floating bathroom scale and put your feet on it. Your feet do not push down on the scale at all. The scale shows that you weigh 0. You have lost your weight—but did you lose your mass? Oh where, oh where, has my weight gone? Oh where, oh where can it be?

ALL MY BODY PARTS ARE STILL TOGETHER—SO I STILL HAVE MASS!

ON A SPACE FLIGHT, YOUR MASS WOULD BE THE SAME; BUT YOUR WEIGHT WOULD CHANGE.

*SUMMING UP MASS AND WEIGHT Your MASS is the amount of material in your body. Your MASS doesn’t depend on where you are. Your WEIGHT is how much your body pushes down on a scale. Your WEIGHT depends on how much MASS you have and where you are.

WHERE WOULD YOU WEIGH THE MOST? Earth Moon OR

*GRAVITY KEEPS OBJECTS IN ORBIT. Orbit- Elliptical path one body travels around another body

* Remember, gravity describes the pull between masses. You have mass, and the earth has mass. There is a pull between you and the earth. We measure this pull with a scale. The more the gravity, the greater the squeeze on the springs of the scale…and the more you weigh.

*GRAVITY AND WEIGHT SUMMARY Your weight on earth is a measure of the GRAVITY pull between you and the earth. Bodies with more MASS produce a greater GRAVITY pull on each other.

ON EARTH So, if I ate a lot of yummy tuna fish while standing on the scale, I would gain mass. The pull between the earth and me would become greater—and I would weigh more!

BACK TO THE MOON During my trip to the moon, my mass does not change, but the moon has much less mass than the earth.

STILL ON THE MOON! There is less gravity pull between you and the moon. If you stood on the scale on the moon— you would weigh less than on earth!

12-2 NOTES FRICTION

REVIEW OF 12.1 Gravity is pulling the Moon toward the center of Earth. Write a brief paragraph explaining why the Moon does not crash into the Earth.(a paragraph is 4-5 sentences)

Gravity is pulling at right angles to the motion of the Moon. The force changes direction in which the Moon is moving, rather than pulling the Moon downward to Earth’s surface. The Moon is in orbit.

List previous experiences you have had walking on different surfaces. Group the experience according to ease of walking.

*FRICTION IS A FORCE THAT OPPOSES MOTION. FRICTION OCCURS WHEN OBJECTS SLIDE PAST EACH OTHER.

FRICTION Definition Characteristics Characteristics Examples Non-Examples Non-Examples Friction

FRICTION: FORCE THAT OPPOSES MOTION CHARACTERISTIC: DIFFERENT SIZES FOR DIFFERENT SURFACES EXAMPLE: PUSHING A HEAVY BOX AGAINST THE FLOOR NON-EXAMPLE: A BOX SITTING ON A TABLE

* Friction – the force that acts to resist sliding between two surfaces. It brings almost everything to a stop. B.There are two types of friction 1. Sliding – Force that resists the motion of an object already moving. 2.Static – keeps an object at rest from moving

*FORCES AND SURFACES FACTORS THAT DETERMINE FRICTION BETWEEN SURFACES TYPES OF SURFACES- FRICTION BETWEEN TWO SURFACES DEPEND ON THE MATERIALS THAT MAKE UP THE SURFACES. MOTION OF THE SURFACES-YOU NEED A LARGER FORCE TO START SOMETHING MOVING THAN YOU DO TO KEEP SOMETHING MOVING, FORCES PRESSING THE SURFACES TOGETHER-THE HARDER TWO SURFACES ARE PUSHED TOGETHER, THE MORE DIFFICULT IT IS FOR THE SURFACES TO SLIDE OVER EACH OTHER

WHICH WOULD RESULT IN GREATER FRICTION, RIDING A SLED DOWN A SNOWY SLOPE OR PULLING IT ACROSS A SIDEWALK?

IS THERE MORE FRICTION BETWEEN A HEAVY WOODEN BOX AND THE FLOOR, OR A LIGHT WOODEN BOX AND THE FLOOR?

WILL IT TAKE MORE FORCE TO MOVE A CHAIR IN POSITION A OR B? WHY OR WHY NOT? A B

*FRICTION AND HEAT AS YOU MOVE AN OBJECT ACROSS THE SURFACE, THE MOLECULES MOVE FASTER AND PRODUCE AN INCREASE IN HEAT. RUB YOUR HANDS TOGETHER VERY FAST! WHAT DO YOU FEEL?

EXAMPLES OF HEAT PRODUCED BY FRICTION

MOTION THROUGH FLUIDS PRODUCES FRICTION. Definition Characteristics Characteristics Examples Non-Examples Non-Examples Fluid

FLUID- A SUBSTANCE THAT CAN EASILY FLOW CHARACTERISTIC: DEPENDS ON THE SHAPE OF MOVING OBJECTS EXAMPLES: GASES AND LIQUIDS NON-EXAMPLES: SOLIDS IN A VACUUM

AIR RESISTANCE Definition Characteristics Characteristics Examples Non-Examples Non-Examples Air Resistance

AIR RESISTANCE- FRICTION DUE TO AIR Characteristic: depends on surface and speed of objects Examples: skydiver jumping from a plane

*TERMINAL VELOCITY- THE VELOCITY AT WHICH A FALLING BODY MOVES THROUGH A MEDIUM, SUCH AS AIR, WHEN THE FORCE OF RESISTANCE OF THE MEDIUM IS EQUAL IN MAGNITUDE AND OPPOSITE IN DIRECTION TO THE FORCE OF GRAVITY.

air resistancegravity

*AIR RESISTANCE When the force of air resistance equals the force of gravity, A skydiver falls at a constant speed. Air resistance differs from friction between solids. Air resistance depends on surface area and the speed of an object in the following ways:

*AIR RESISTANCE 1.) An object with a larger surface area comes into contact with more molecules as it moves than an object with a smaller surface area. This increases air resistance. 2.) The faster an object moves through air, the more molecules it comes into contact with in a given amount of time. As the speed of the object increases, air resistance increases.