Download Chapter 1: Matter in Motion Section 1: Measuring Motion A

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 Earth’s 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 =
50𝑚
10𝑠
= 5 𝑚/𝑠
Standard units (SI) for speed is meters per second (m/s).
Other commonly used units are:
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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
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Is like an object’s rate of change of that objects position
If speed and direction don’t 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
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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
𝐴𝑣𝑒𝑟𝑎𝑔𝑒 𝐴𝑐𝑐𝑒𝑙𝑒𝑟𝑎𝑡𝑖𝑜𝑛 =
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𝑓𝑖𝑛𝑎𝑙 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦 − 𝑠𝑡𝑎𝑟𝑡𝑖𝑛𝑔 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦
𝑡𝑖𝑚𝑒 𝑖𝑡 𝑡𝑎𝑘𝑒𝑠 𝑡𝑜 𝑐ℎ𝑎𝑛𝑔𝑒 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦
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 it’s 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
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Force has size and direction
Newton: the SI unit for force, symbol is N
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All forces act on objects
Forces do not always cause motion
 Example: you are exerting a force on your chair, however the chair doesn’t move. That is
because the floor is exerting a force on the chair 
You cannot see all forces! For example the air around you is held near Earth’s surface by the force of
gravity.
Net Force: the combination of all of the forces acting on an object
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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.
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Can cause a moving object to slow down or eventually stop
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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
 Mount depends on how the surfaces move
 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
 The force of the friction is balanced with the force applied
 Can be overcome with a large enough force
Ways to Reduce Friction:
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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:
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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
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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 – a British scientist
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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)