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Chapter 1: Matter in Motion Section 1: Measuring Motion A Reference Point is: an object that appears to stay in place When an object changes position overtime relative to a reference point, the object is in motion. Motion can be north, south, east, west, up and down. Common reference points are: the Earthβs surface, trees, buildings, and sometimes other moving objects Speed: the distance traveled divided by the time interval during which the motion occurred Example: Time = 10s and Distance=50m Speed = 50π 10π = 5 π/π Standard units (SI) for speed is meters per second (m/s). Other commonly used units are: ο· ο· ο· Kilometers per hour (km/hr) Feet per second (ft/s) Miles per hour (mi/h) Not everything moves at a constant rate though so you need to be able to calculate average speed. Average Speed =total distance total time Speed on a Graph: shown on a graph of distance versus time Velocity: the speed of an object in a particular direction ο· ο· Is like an objectβs rate of change of that objects position If speed and direction donβt change then velocity is constant, so constant velocity is motion along a straight line Resultant Velocity: is a combination of 2 or more velocities (See Figure 4 on page 7) Acceleration: the rate at which velocity changes over time ο· ο· ο· ο· An object accelerates if its speed, direction or both change Positive acceleration means an increase in velocity Negative Acceleration means a decrease in velocity or what is called deceleration The faster the velocity changes, the greater the acceleration is π΄π£πππππ π΄ππππππππ‘πππ = ο· πππππ π£ππππππ‘π¦ β π π‘πππ‘πππ π£ππππππ‘π¦ π‘πππ ππ‘ π‘ππππ π‘π πβππππ π£ππππππ‘π¦ Acceleration is measured in meters per second per second, or m/s2 Circular Motion: An object traveling in a circular motion is always changing its direction so its velocity is always changing, so itβs accelerating. This is called centripetal acceleration Section 2: What is a Force? Force: a push or pull exerted on an object in order to change the motion of the object ο· Force has size and direction Newton: the SI unit for force, symbol is N ο· ο· ο· All forces act on objects Forces do not always cause motion ο§ Example: you are exerting a force on your chair, however the chair doesnβt move. That is because the floor is exerting a force on the chair ο You cannot see all forces! For example the air around you is held near Earthβs surface by the force of gravity. Net Force: the combination of all of the forces acting on an object ο· ο· ο· ο· ο· When forces are moving in the same direction, you add them together When forces are moving in opposite direction you subtract the smaller force from the larger one. When the forces on an object produce a net force of 0N, then those forces are balanced Balanced forces do not cause a change in motion of an object When the Forces of an object are not 0N, the forces are unbalanced and a change in motion occurs. Section 3: Friction: A Force that Opposes Motion Friction: a force that opposes motion between two surfaces that are in contact. ο· Can cause a moving object to slow down or eventually stop ο· ο· Occurs because the surface of any object is rough Two factors that affect the amount of friction are 1) the force pushing the surfaces together and 2) the roughness of the surfaces. o If the force pushing objects together increases then the hills and valleys come in closer contact and the friction increases o The rougher the surface, the greater the friction is Two Types of Friction 1. Kinetic Friction: friction between moving surfaces ο· Mount depends on how the surfaces move ο· Sliding objects experience more friction than rolling objects 2. Static Friction: when a force is applies to an object but does not cause the object to move ο· The force of the friction is balanced with the force applied ο· Can be overcome with a large enough force Ways to Reduce Friction: ο· ο· ο· Lubricants: substances applied to reduce friction between objects (motor oil, wax, grease, air on a hockey table, etc) Switching from sliding to rolling friction (using ball bearings in wheels) Make surfaces that rub together smoother (sanding wood surfaces) Ways to increase Friction: ο· ο· Make surfaces rougher (sand on ice, textured batting gloves, etc) Increase the force pushing the surfaces together (pressing harder on sandpaper) Section 4: Gravity: A Force of Attraction Gravity: a force of attraction between two objects that is due to their masses ο· ο· ο· Gravity is a result of mass, so matter is affected by gravity Objects experience a pull toward all other objects, called gravitational force Because Earth has such a large mass, it also has a very large gravitational force, pulling everything toward its center Sir Isaac Newton β a British scientist ο· ο· ο· Proposed the idea of gravity He said that an unbalanced force on apples caused them to fall from trees, and that an unbalanced force on the moon kept it circling the Earth; and that both of these forces were really the same, a force of attraction called gravity Wrote the Law of Universal Gravitation, which describes the relationships between gravitational force, mass, and distance Law of Universal Gravitation: 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 the objects. Two Parts: 1. Gravitational Force Increases as Mass Increases 2. Gravitational Force Decreases as Distance Increases Weight: is a measure of the gravitational force on an object; SI unit is Newtons (N) Mass: is the amount of matter in an object; SI unit is a kilogram (kg) but is also measured in grams (g) or milligrams (mg)