MOTION AND GRAVITY - MYP YEAR 3 FALCONS - Home
MOTION AND GRAVITYOBJECTIVESDescribe motion in terms of distance, speed & velocity.Give word definition and a formula for acceleration & deceleration.Explain why circular motion involves acceleration.State Newton’s three laws of motion and give examples of each.Relate the concepts of acceleration of a falling object and gravity.State Newton’s law of universal gravitation.MotionSo we talk about motion. But what is motion? Simply put, motion is a change in position. Motion is caused by a force acting on an object.We measure motion in terms of distance. We say an object has gone a certain distance when we talk about motion.Distance is the length between two places. In the metric system, distance is measured in meters and kilometers.SpeedIf we measure how long an object takes to go a certain distance, we have speed.Speed is the distance an object travels over a certain amount of time.The formula for speed is S = d/t.Speed can be expressed as miles/hour (mph), kilometers/hour (kph), miles/second, or meters/second.VelocityNow that we have defined speed, the only thing we don’t know is the direction. If we know the speed of an object, and we know the direction that the object is moving in, we use a term called velocity.Velocity is a term used to express both the speed and direction of an object.Velocity is measured in kilometers per hour or meters per bining VelocitiesIf you are rowing a boat down a river at 16 mph, are you going 16 mph or not?The answer is that you are moving faster than 16 mph because the stream is also moving. To find the total velocity IN THE SAME DIRECTION you would ADD the velocities. If you were rowing against the current, you would SUBTRACT the velocities.AccelerationAcceleration is the rate of change in velocity; the acceleration of an object is equal to its change in velocity divided by the time during which this change occurs.The formula for acceleration is: A = v/tDeceleration is sometimes called negative acceleration because it decreases acceleration.Example: If a car goes from 0 m/sec to 40m/sec in 10 seconds, what is its acceleration?Answer: 4 m/sec/secThis means that for every second the car is traveling, it is picking up speed at the rate of 4 m/sec.Circular MotionWhen an object is moving in a straight line, acceleration and deceleration are easy to recognize. When an object is moving in a circular path, it is constantly changing direction.If the object is constantly changing direction, so is its velocity. If an object continually changes its velocity, it is accelerating.A planet that is in orbit is constantly accelerating since its velocity is constantly changing and its orbital speed is constant.FORCES AND WORKFORCEA push or pull exerted on an object that causes it to start moving, stop moving, or change its motion.WEIGHTThe amount of force the earth’s gravity exerts on an object.FRICTIONIn ancient times scientists believed that an object that was in motion would stay in motion until the force was removed.Later on scientists discovered that this was not entirely true. An object in motion comes to rest not because there is no force acting on it, but because of friction.Friction is the force that opposes the motion of an object.Friction always acts in the direction opposite of the direction of the force.TYPES OF FRICTIONSliding FrictionRolling FrictionFluid FrictionSliding Friction Sliding friction happens when one object slides on top of another.The amount of friction depends on the weight of the objects and the type of surface they are sliding over.Rolling FrictionRolling friction happens when a round object, like a ball, rolls over a surface.The amount of friction produced by this type of motion is less than sliding friction.Fluid FrictionFluid friction happens when an object moves through a fluid or air.This type of friction is less than sliding friction.Lubricants are used reduce friction in machinery. Airplanes are designed to reduce the friction of the air as they fly.Forces in FluidsFluids produce a friction called fluid friction. Another important force in fluid is pressure.Pressure is the push that is exerted on a certain area.Air pressure, water pressure, and oil pressure are examples of pressure.WORKIn science, the term work has a very special meaning. Whenever a scientist discusses forces and pressures, they will usually talk about work.Work is a force acting through a distance.Whenever you push, pull, or throw something, you are performing work.Laws of MotionSir Isaac NewtonConsidered to be one of the greatest scientists in history. He was a mathematician and a scientist who made many contributions to science and math.He was born in January of 1643 in a small town in England. In 1661 he went to college and got his college degree in 1665. In 1668 he got his masters degree. He was an individualist who didn’t like to run with the crowd, but to go out on his own. He was very interested in math and philosophy.His first great contribution to math came in 1666 when he developed a math known today as calculus.Newton was also very interested in optics, the study of light. He tried to explain how colors occurred and came across the discovery that natural sunlight consists of all the colors. He proved this by passing a beam of light through a prism.What Newton is best known for was his work in physics. He was asked by a friend, Edmund Halley (of Halley’s comet fame) to help him solve the problem of orbital motion. While in college, Newton did some work on the subject but never finished it. Now with his friend, he had the chance to do some more work.For the next two and a half years, Newton worked hard and finally came up with his Three Laws of Motion, and the description of the force that controls these laws.The results of all this work was published in a book in 1687. What Newton could not have known was the imp[act his book would make on the world of science. His life had changed so much that in 1693 he suffered an emotional breakdown. His health was regained, but his creativity was not. Never again would Newton enjoy the creative successes he enjoyed in his earlier life.Through his political connection in the English court, Newton held a number of high-ranking positions until his death in 1727.First Law of MotionAn object in motion tends to stay in motion, and an object at rest tends to stay at rest, unless the object is acted upon by an outside force.This means that if you leave your books on the desk overnight, it will still be there in the morning unless some force caused it to move. This also means that a kicked soccer ball will travel in a straight line until it either hits something or something forces it to slow down.We feel the effects of Newton’s First Law everyday. In a moving vehicle we travel at the speed of the vehicle. When it comes to a stop, we are “pushed” forward.This law of motion also explains why it is so important to wear seat belts. If you were traveling at 60 mph, and were not wearing a seat belt, and the car hit a cement wall, the car would stop.You, on the other hand, would not stop. You are still traveling at 60 mph and you would probably go through the windshield. You would not stop until you hit the ground.You also feel the effects of this law when you go around a curve, or turn, too fast. Even though the car has turned, you body wants to keep on going in the same direction it was. In this case, you are inside the car, so you have no choice but to turn with the car. Your body, on the other hand, feels the effect of this change in motion.Newton developed a term for an objects tendency to stay in motion or at rest. He called it inertia.Inertia is the tendency of an object to remain still or stay in motion.This law also explained that a force is required to overcome inertia. That in order to start something moving or stop something moving, a force must be applied.Second Law of MotionThis law relates mass, acceleration and force.This law relates to acceleration.This law says that the acceleration of an object is related to its mass and the amount of force used to move the object.It is not so much a law than a formula: F = maWe all know that if we hit as tennis ball with a tennis racquet, the tennis ball will fly off the racquet. If we were to try that with a bowling ball, we would need a new racquet. This is because we know that a bowling ball has more mass. So we know that acceleration is related to force and mass.Newton calculated that the amount of force needed to move an object is the product of its mass times the acceleration of the object.Let’s suppose that Mike’s car is out of gas.It weighs 1,000 kg.Mike wants to push the car at 0.05m/sec.How much force does Mike need to apply to the car?F = maThis law also explains why little cars can accelerate faster from a stop light than a big truck and why little boats can slow down and stop quicker than big super tankers.Third Law of MotionFor every action, there is an opposite and equal reaction.This is the most famous of the three laws.It is the one we experience every single day.A baseball player depends on this law in order to be successful.A batter swings at the ball.He hits the ball with a certain amount of force (the action).The ball goes in the opposite direction, hopefully out of the park (the reaction).This law is the most important one for space travelers.With no friction to slow them down, a spacecraft needs very little force to get it moving.Then Newton’s First Law takes over and the spaceship moves in a straight line until it bumps into something, or something bumps into it.MomentumAll moving objects have momentum. Momentum is the product of an objects mass multiplied times its velocity.The formula for momentum is M = mv.This explains why it is easier to stop a baseball going 90 mph than a freight train going 90 mph. They both have the same velocity, but the mass of the freight train is by far greater than a baseball.Gravity and MotionBefore Newton did his work on the laws of motion, an Italian scientist was already doing experiments on motion and gravity. Legend has it that Galileo took two cannonballs to the top of the Leaning Tower of Pisa. They were both the same size but on weighed ten times more than the other.He dropped them off the edge of the tower at the same time.People believed in those days that if an object weighed more than another, it would travel faster if it was dropped.In Galileo’s experiment, both balls hit at the same instant.What is important about this is that Galileo was able to come up with the theory that all falling objects accelerate at the same rate regardless of their mass.In other words, weight has nothing to do with acceleration.Objects fall at the rate of 9.8m/sec/sec. This means that for every second the object is falling, its velocity is increasing by 9.8 m/sec.For example, if you were to drop a penny off a tall building, it would be traveling at 49 m/sec after five seconds.This rate of acceleration is not always observed.We know that something like a feather or a parachute will slow an object down.In the case of a parachute, this is a desired effect. We know that the air has a great resistance on an object falling. All objects will meet with some resistance, no matter how light they are. As a result, they will accelerate to a certain point and not accelerate any more. This is called an object’s terminal velocity.GravityWe all know that gravity is what keeps us on the planet.It makes objects “fall” to the earth and gives us our weight. What many people do not know is that gravity is a force of attraction.Both Galileo and Newton believed that it was the earth that caused objects to fall toward it.It was Newton who came up with the correct theory as to why.Newton understood that the earth has a mass to it; it’s a large body.Because of this mass, the earth attracts lesser object to it.The closer to the object, the greater the attraction.We call this attraction gravity.Newton also went further with his theory. He formulated his Universal Law of Gravitation which stated that a gravitational force is present between any two objects.That the size of the force depends on the masses of the objects and the distance between the two objects.The further away from the object you get, the less the force of attraction is.This explains why astronauts get weightless in outer space; they are beyond the attraction of the earth.It’s this Law of Universal Gravitation that helps explain why planets and moons stay in orbit.The largest object in our solar system is the sun.The sun’s gravity is pulling the earth toward it.The earth’s acceleration in space is just enough to keep it from moving from the sun and spinning off into space. ................
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