Chapter 3: Motion and Forces

Section 1-

Reference Point-Lets you know an object is in motion by comparing it to another point.

-Speed-The rate of change in position.
-Instantaneous Speed-is the rate of motion at any given instant (just like a picture)
-Contant Speed-A speed that does not vary.
-Average Speed- Is the total distance traveled divided by the total time of travel. (distance/time)
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Speed & Velocity

-velocity
.speed in a given direction
.can change even when speed is constant

Acceleration
.the rate of change in velocity
.change in speed or direction
(slowing down-negative acceleration)

a=
vf-vi
t
a=acceleration
vf=final velocity (end)
vi=initial velocity (start)
t=time
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Graphing Motion

Distance-Time Graph
x axis=Time
y axis=Distance

.slope=speed
.steeper slope=faster speed
.straight line=constant speed
.flat line=no motion

Distance-Speed Graph
x axis=Time
y axis=Speed

.slope=acceleration
.straight line=constant acceleration
.flat line=constant velocity
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NEWTON'S FIRST LAW OF MOTION

.An object will not change its motion unless a force acts on it.
.An object that is not moving remains at rest until something pushes or pulls it.
.An object that is moving remains moving until something pushes or pulls it.
.The force that causes objects to slow down is friction.
.Friction always acts opposite to the direction of motion.
.To keep an object moving when friction is acting on it, you have to keep pushing or pulling on the object to overcome the frictional force.
.All objects resist having their motion changed.
.This tendancy to resist a change in motion is called inertia.
.The more mass an object has, the greater its inertia.
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Force

-Force
.a push or pull that one body exerts on another.
-Balanced Forces
.forces acting on an object that are opposite in direction and equal in size.
.no change in velocity
-Net Force
.unbalanced forces that are not opposite and equal.
.velocity changes(object accelerates)
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Gravity

.a force that pulls bodies of mass together.
-Weight
.A planet's gravitational pull on an object. This give the object weight.
-Mass

.the amount of matter that an object contains.

.Gravity&& the Scale
.Gravity pulls an object down and a scale measures the pull.
.Earth keeps us on the ground
.Earth's gravity pulls us toward the center of the planet
.Things with mass
.Planets, stars, moons
.Weigh less on moon?
.moon has less mass, less gravity-less pull, less weight
*anything that has [mass], has [gravity]