Chapter 1 Matter in Motion

Matter in Motion UnitChapter ObjectivesDescribe the circular motion of a moving object as the result of a force acting toward the center.Given an object in motion, calculate its speed (distance/time).Interpret a line graph representing an objects motion in terms of distance over time (speed) using metric units.Explain every object exerts a gravitational force of attraction on every other object.Recognize an objects weight is a measure of the gravitational force of a planet/moon acting on that object.Compare the amount of gravitational force acting between objects (which is dependent upon their masses and the distance between them).

What is MotionMotion occurs when an object changes position over time compared with an object that appears to stay in place?????? I know it sounds kind of weird. Heres another way to look at it. When we see something that appears to be moving our eyes are actually picking up on a couple of things. One, obviously the object that is moving, and two an object that appears to be still. The object that appears to be still or not in motion is known as a reference point. (Just because it appears to not be in motion doesnt mean its not in motion.)Motion continuedMotion is usually described with a direction like north, south, east, or west.Sometimes its not easy to determine if an object is in motion.Reference PointsAs we have already pointed out a reference point is an object that appears to stay in place. The most common reference point is the earths surface(buildings, trees, and mountains).A moving object can also be a reference point. Speed!!!!Speed is the rate at which an object moves. Most of the time we think of speed as MPH, but the common SI unit is m/s(meters/second)Speed is distance/time.Average speed is determined by simply taking the total distance the object moved and dividing it by the total time.VelocityLots of times we get velocity mixed up. It is commonly associated with speed. Velocity is the speed of an object in a particular direction and is expressed in m/s. So how are they different??? Speed is the rate at which an object moves. It doesnt have to include direction. Velocity on the other hand must include direction. Speed and Direction Affect VelocityIf either the speed or direction of an object changes then the velocity changes. So if an object is going in a straight line at a constant speed is velocity changing?Combining VelocitiesWhen you combine two velocities that are in the same direction, add them together to find the actual velocity.When you combine two velocities that are in opposite directions, subtract the smaller velocity from the bigger velocity.

AccelerationThere is a misconception about acceleration. It is commonly thought of as speeding up. That is not so in science.Acceleration is the rate at which velocity changes. So any time you change your speed or your direction, not only do you affect your velocity, but you also affect your acceleration.

Calculating AccelerationAcceleration equals Final velocity starting velocity all divided by time it takes to change velocity.Because acceleration examines the rate(time) at which velocity(m/s) changes it is expressed in m/s/s. So suppose a bicycles acceleration is 3m/s/s. that means that every second your southward velocity increase by 3m/s.

Acceleration ExamplesAcceleration in which velocity increases is known as positive acceleration.Acceleration in which velocity decreases is known as negative acceleration or deceleration. Continuous AccelerationThe acceleration that occurs due to a circular motion is known as centripetal acceleration. Ex. The blades of a windmill constantly change direction as they travel in a circle. ForceForce is a push or a pull on a object.All forces are exerted by one object on another.It is expressed in newtons (N). The greater the newtons the greater the force.Just because a force is exerted on an object doesnt mean that motion will occur. GravityYou constantly have an unseen force on you.Earth is a massive object in space, and because of this it exerts gravity on you and every object on Earth. Net ForceA force that occurs from combining all the forces exerted on an object. If forces are applied in the same direction then you add the forces together to get the net force. If forces are applied in opposite directions then you subtract the lower force from the higher force to find the net force. Unbalanced vs. Balanced Forces Once you have figured out the net force applied to an object then you can determine whether the forces were balanced or unbalanced. In other words whether it moved or not.If the net force applied to the object is greater than zero then the forces are unbalanced. In this case the object would be in motion.If the net force applied to the object is zero then the forces are balanced. In this case the object wouldnt be in motion. What is Friction?Friction is a force that opposes motion between two surfaces that are touching.When a baseball player slides into second base he/she is experiencing friction. If they werent they would just keep on sliding on past second base.

Why does friction happen?Friction occurs because the surface of any object is rough. Your desk, even though it may look smooth, if viewed through a microscope you would notice several bumps or ridges. These bumps and ridges are what oppose the motion of your hand across the desk.There are many factors that affect the amount of friction that may occur.Factors that affect frictionHow rough a surface is. This is basically common sense here. Which would you rather fall on? Ice or Pavement? I would take ice any day. This is because the rougher the surface the more friction.How much of a force is applied to an object.Lets say we had two boxes on the floor. In one box I filled it with feathers. In the other box I filled it with bricks. Which one is going to be easier to push across the floor? With out a doubt the feathers. There is less friction with the box of feather due to there being lesser force.

Types of FrictionSliding FrictionVery effective at opposing the movement of an object.When you go sledding in the winter you are using sliding friction. The baseball player sliding into second is another example.Rolling FrictionHelps reduce the amount of friction.Lets take the same box of bricks I talked about earlier and put them on a cart with wheels. Pushing them across the floor would become a lot easier. This would be an example of rolling friction. Types of FrictionFluid FrictionFirst of all, a fluid can be water, milk, oil, and even air.Where would it be easier to run in a pool or out of a pool? Fluid friction is the opposition by some fluid like water or even air. In fact both rolling friction and fluid friction go against a vehicles gas mileage. Why? Static FrictionThis is where a force is applied to an object and that object doesnt move. That like you going up to my wall and pushing it. It doesnt matter how hare you push. Unless you are Hercules you are not pushing that wall anywhere.Friction can be Harmful or HelpfulHarmful Take this example. Your brother has truck with factory tires on it that gets about 16 MPG. He then decides to put new mud tires on it. Now that same truck gets about 10 MPG. He will now have to buy gas more often.HelpfulUse the same example, same situation. With the factory tires your brother was noticing he was getting stuck in the mud a lot. He gets the new mud tires and now he can drive out though the muddiest of fields without getting stuck.Ways of Reducing FrictionLubricantsSubstances that are applied to surfaces to reduce the friction between them. Oil, wax, and greaseSwitch from sliding to rolling frictionMake the surfaces that are making contact smoother.Ways of increasing FrictionMake the surfaces rougher.Increase the force applied to the two surfaces.

GravityGravity is a force of attraction between objects that is due to their masses.Gravity is a result of mass.All things that have mass exert gravity.We, for example, have mass so therefore we exert gravity.Wait a minute!!!??? If we exert gravity why arent object coming at us???Earth is the most massive object that is closest to us, so everything on earth is attracted to earth by gravity. Earth Large ForceEarth is so large that everything on it is attracted to its surface. So in order for something to be moved away from earths surface that object must have a force applied to it greater than what Earth is applying to that object.Law of Universal GravitationDeveloped by Sir Isaac Newton due to an apple falling out of a tree and clocking him on the head (not really).The story goes that Newton was observing an apple falling from a tree. He recognized that an unbalanced force was drawing it down to Earth. He realized this force was gravity.He developed his observations into a law that states: All objects in the universe attract each other through gravitational force. The size of the force depends on the masses of the objects and the distance between them.The LAW Part 1Gravitational Force Increases as Mass Increases.If the only two things that existed in outer space were an elephant and a mouse then the mouse would be pulled towards the elephant by the elephants gravity because of its greater mass.To put it in more realistic terms. The moon is attracted to the Earth because the Earth has a greater mass. So why doesnt the moon come crashing into the Earth?The LAW Part 2Gravitational force decreases as distance increases.Heres a fact for thought. The sun is 300,000 times more massive than the Earth. So why arent we attracted to the sun? It is because of the distance from the sun. We are so far that the suns gravity is cancel out by the Earths gravity.

WeightWeight is a measure of the gravitational force exerted on an object.Have you every hopped on that scale at kmart or any other place that has one that gives you your weight on earth and on the moon? If you have then you noticed that your weight on the moon was smaller than that of Earths. That is because applies a greater gravity due to its greater mass. Weight and Mass are DifferentWeight of course is the measure of the gravitational force exerted on an object.Mass is the amount of matter in an object.Your weight changes from the Earth to the moon. But your mass doesnt unless you lose a leg or an arm while on your trip to the moon.