WERE DONE WITH CHEMISTRY! NO MORE: Chemical Equations Writing Formulas Periodic Table Cations & Anions Chapter 10: Motion Section 1 Measuring Motion Definition: physics the study of interactions between matter and energy. The science of physics is used to explain almost every common event: And the concept of MOTION is extremely important in physics! Physics: It Explains the Universe Motion may seem to be very simple, but there are scientific concepts that can explain it. Definition: motion - an objects change of position over time. There are two ways to measure how far an object has changed position: Distance & displacement Definition: distance - a measure of the entire path of an object. Definition: displacement - a measure of an objects change in position from start to end. Displacement is ALWAYS a straight line! Distance vs. Displacement We can also measure how fast an object changes its position Definition: speed the measure of how fast an object is moving. Speed equals distance/time (s = d/t) The SI Unit for Speed is meters per second: (m/s) Americans usually measure speed in mph (miles per hour) Mph OR mi/h What in the world is velocity? Definition: velocity the speed of an object in a certain direction. alwaysdirectionVelocity always has a direction! Velocity equals distance/time (v = d/t) Velocity is calculated the same way as speed! The velocity (speed) of an object measures how quickly it is changing position. For example: a speed of 10 m/s means that the object will move 10 meters after one second. A speed of 60 mph means that an object will move 60 miles in one hour. Its actually just common sense. Lets look at an examples A runner runs 50 meters East in 10 seconds. d = 50 m t = 10 s v = d/t = 50 m / 10 s v = 5 m/s East EASY. AS. PIE. Examples Lets look at an example A biker is riding north. After 10 seconds, he has gone 100 meters. d = 100 m t = 10 s v = d/t = 100 m / 10 s v = 10 m/s North EASY. AS. CAKE. Examples Chapter 10 Section 2 - Acceleration You may not realize it, but you are familiar with the term acceleration Definition: acceleration the change in velocity over time. Acceleration has the derived unit of m/s 2. (meters per second squared) An object accelerates when it speeds up OR slows down. Acceleration tells how quickly an object is changing velocity. So, you need the change in velocity over a time period. Acceleration = (final velocity minus initial velocity, divided by time.) a = (v f v i ) t Seriously, what IS acceleration? Think of it like thiswhen you accelerate You are moving more or less m/s for every second that passes. So, if you began with a velocity of 10 m/s north and you had an acceleration of 2 m/s 2 N, then that means For every 1 second that passes, you are moving 2 m/s faster! What IS acceleration? So, after 5 seconds, you are moving 10 m/s faster the new velocity would be 20 m/s N Its not a hard concept to understand What IS acceleration? Lets look at an example A biker is riding north at a velocity of 3 m/s. After 10 seconds, his velocity has changed to 9 m/s north. What was his acceleration? v i = 3 m/s north v f = 8 m/s north t = 10 seconds a = = = EASY. AS. CAKE. Examples 8 m/s 3 m/s 10 s 5 m/s 10 s.5 m/s 2 Acceleration can be a negative number. This means that the velocity is decreasing. (the object is slowing down) It could also mean that the object is speeding up in reverse. You have a negative acceleration when you apply the brakes and slow down at a stop sign. Object that have a constant velocity have no acceleration. If the velocity isnt changing, then there is no acceleration! Objects with a constant acceleration are speeding up by that much each second. In other wordsmoving faster & faster & faster Acceleration is also a change in direction. Since velocity involves speed & direction, acceleration must involve direction also. Definition: centripetal acceleration the constant change of direction of an object moving in circles. An object can be moving at the same velocity when traveling in a circle, but its direction is always changing. So, it is accelerating! Chapter 10: Motion Section 3 Motion & Forces The term force is used all the time, but it can be hard to describe Definition: force a push or pull that makes an object accelerate. Forces have directions! What is a force? An object can only change its direction when a force is applied to it! Some examples of forces: Gravity Friction Electric Force Nuclear Force Magnetic Force Centrifugal Force Centripetal Force Circular Motion Forces Definition: centripetal force pulls an object toward the center of rotation. Definition: centrifugal force moves an object away from the center of rotation. There are two types of forces: Balanced and Unbalanced. Definition: balanced forces a pair of forces that are equal and opposite. Balanced forces cannot change an objects acceleration. When 2 forces cancel each other out, they are balanced. Object Force A Force B This object wont move anywhere! Definition: Unbalanced forces a pair of forces in which one force is stronger than the other. Unbalanced forces cause objects to accelerate. Object Force A Force B This object will move to the right! Friction is a force present when any two objects are in contact. Definition: friction a force that causes resistance to motion when objects are in contact. Friction tries to slow down moving objects. Friction can be described as static or kinetic. Static friction exists between two objects that are not moving. Kinetic friction exists between two objects that are in motion. Friction comes in several great-tasting flavors: Dry Friction: between two solid surfaces. Sliding Friction one object is forced to move across another. Rolling Friction an object rolls across a surface. Fluid Friction: involves a liquid or gas. Air friction between a gas & a liquid or solid. Friction isnt always a BAD thing.