Forces Motion Did you know if you go

Forces & Motion Did you know if you go up higher than 20, 000 feet you are classified as an astronaut?

Gravity & Motion n In 400 BCE, Aristotle thought that the size of the object made a difference in how fast it falls If you asked Aristotle if a marble and a baseball fell at the same time, Aristotle would say the baseball. Aristotle never tested his theory

Along comes Galileo n n n In the late 1500’s, Galileo questioned Aristotle’s ideas. Galileo took two _____ of different sizes and dropped them off the Leaning Tower of Pisa Guess what – they both landed at the same time. Does anybody know how Galileo came up with the this idea? ____ of different sizes hitting the ground at the same time during a storm.

Gravity and Acceleration n Objects fall to the ground at the same rate because the acceleration due to gravity is the ______ for all objects Acceleration depends on both ______ and _______ Heavier objects have greater mass but it takes more to accelerate them and smaller objects do just the opposite

Acceleration Due to Gravity n n Acceleration is the rate at which _____ changes Acceleration = change in velocity/change in time Any change in science is denoted by a triangle referred to as a ______ Δ

Question Time The acceleration rate due to gravity is the same no matter what the object’s size or mass. a. yes b. no n Acceleration depends on a. mass b. gravity c. volume d. both a and b e. both a and c. e. all of them n Acceleration is the rate at which _______ changes. a. gravity b. mass c. velocity d. volume n

Velocity of Falling Objects n n n n Δv = g x t Gravity is usually referred to as 9. 8 m/s² Change in velocity is the difference between starting velocity and final velocity Net _____ is the force of gravity – force of air resistance Air resistance is the force that opposes motion of an object through air Air resistance depends on the _____, ______, and ______ of the object Air resistance is the result of friction between the falling object and the air, and the inertia of the

Acceleration Stops at Terminal Velocity n n n When upward air resistance equals downward force of gravity, a constant velocity is reached. This constant velocity is referred to as _____ velocity Terminal velocity can be a good thing. – If there was no air resistance, hail would fall at a rate of 350 m/s instead of 5 and 40 m/s

Parachuting n n n Parachuting is a good example of how terminal velocity works The 1 st parachute was regularly used by Jacques ____ in 1797 The first jump was from 3200 feet and the last over 8, 000.

Science Humor n n When asked why he wasn’t interested in being a paratrooper, an Army pilot said, “I will never understand why anyone would want to jump out of a perfectly good airplane. ”

Free Fall & Orbiting Objects n n n Objects are only in ______ when there is no force other than gravity acting on them Free fall can only occur in a vacuum A vacuum is a place where there is ____ matter Orbiting objects are in free fall ____ is a measure of gravitational force The size of the force depends on the ____ of objects and the ____ between them

Question Time n n n The force of gravity – air resistance is known as a. final velocity b. terminal velocity c. net force. Air resistance depends on everything except a. mass b. shape c. size d. speed When air resistance equals gravity, a. final velocity b. acceleration c. terminal velocity is reached. An object is in freefall when only a. air resistance b. Net force c. terminal velocity d. gravity is acting on the object. Mass is a measure of gravitational force. A. yes b no The size of gravitational force depends on the a size of the objects b. the distance between the objects c. the force the object’s exert d. a and b e. all of the above.

How an Orbit is Formed n n The space shuttle moves forward at a constant speed Gravity pulls the shuttle down toward earth The two forces cause the shuttle to follow the curve of the Earth’s surface. (25, 000 mph and 150 km above earth) Astronauts ______ in space because they are in a free fall.

Orbiting and Centripetal Force n n _____ force that moves in a circular path Means toward the center

Projectile Motion & Gravity n n The ______ path an object follows when it is thrown or propelled near the surface of the earth Has both a _____ and ______ component Components are _____ of each other The two components combined create the curved path

Examples of Projectile Motion n n Leaping frog – bullfrogs are the largest frog in the US – there hind legs can be up to 25 cm long – longer than the bullfrog itself Water sprayed from a sprinkler Swimmer diving into water Arrow shot by an archer

ANSWER me THIS n The moon has no atmosphere. What do you think would happen if an astronaut on the moon dropped both a feather and a hammer at the same time from the same height? n Whenever Jon delivers a newspaper to the Zapanta house, the newspaper lands in the bushes, as shown below. What should Jon do to make sure the newspaper lands on the porch? n A rock at rest falls off a tall cliff and hits the valley below after 3. 5 s. What is the rock’s velocity as it hits the ground?

Question Time n n Orbits are created by a. gravity b. constant speed c. terminal velocity d. acceleration e. a and b f. c and d An unbalanced force that moves in a circular direction is a. centripetal b. centrifugal force. The curved pathway an object follows when propelled is called a. centripetal motion b. projectile motion c. tangential motion. Projectile motion has both a horizontal and vertical component that is independent of each other a. yes b. no

Horizontal Motion n n ______ effects this component. Once an object leaves your hand, it’s velocity is constant It is not affected by gravity Mathematical concepts called vectors are often used to describe horizontal motion

Vectors n n n Tell us the _____ movement occurs Tell us the _____ of the object Vertical vectors show increasing velocity downward

Vertical Motion n _____ causes a falling object to have vertical motion If you ignore air resistance, all objects will fall at a rate of 9. 8 m/s² If you are throwing a projectile, you must always aim ____ than your target to hit what you are aiming at.

Time to Summarize n n n n Gravity causes all objects to accelerate towards earth at a rate of 9. 8 m/s² Air resistance slow the acceleration of falling objects. An objects falls at its terminal velocity when the upward force of air resistance equals the downward force of gravity A object is in freefall if gravity is the only force acting on it Objects in orbit appear to be weightless because the are in free fall A centripetal force is needed to keep objects in circular motion. Gravity acts as a centripetal force to keep objects in orbit Projectile motion is the curved path an object follows when thrown or propelled near the surface of the earth Projectile motion has two components – horizontal motion and vertical motion. Gravity affects only the vertical motion of projectile motion.