Mr. McMartin
Beta Pod Science
 The movement now called the Scientific Revolution
took place between the 16th & 18th centuries.
Mainstream science of the time still taught the
Aristotelian view of the universe. With the translation
of Greek, Roman, and Arabic texts and the
improvement of the printing press, ideas that are now
the basis of modern science first became available to a
large number of people.
 In astronomy, the theory that the sun is the center of
the solar system was proposed by Copernicus. Galileo
laid the foundations of the principles of mechanics
(the study of motion) and first turned a telescope
toward the sky. Philosophers such as Descartes began
to develop the idea of nature as a complicated system
of particles in motion.
 Sir Isaac Newton (1642-1727) was a central figure in the
Scientific Revolution during the 17th century. He was
born 1642, the year Galileo died.
 Remember that acceleration, like velocity, always
includes direction. However the relationship between
acceleration and motion differs from the relationship
between velocity and motion. An object’s motion is
always in the same direction as its velocity. But an
object’s motion is not always in the same direction as
its acceleration.
 Ex. When an object is in circular motion, its
acceleration is toward the center of the circle, but its
motion is not.
 You might think that the motion of an object is easy to
detect- you just watch the object right?
 You are actually watching the object in relation to
another object that appears to stay in place.
 The object that appears to stay in place is the
“reference point”
 When an object changes position over time relative to
a reference point, the object is in “motion.”
 The earth’s surface
 Trees
 Buildings
 Moving objects in relation to one another.
 Ex. If you were in a hot air balloon and you saw a bird fly
buy.
 Speed: the distance traveled by an object divided by
the time taken to travel that distance.
 The SI unit for speed is meters per second or m/s
 Other commonly used speeds
 Kilometers per hour (km/hr) or kph
 Feet per second (ft/s) or fps
 Miles per hour (mi/hr) or mph
 Most of the time, objects do not travel at a constant
speed.
 Ex. You do not walk at a constant speed from one class to
the next.
 Here is the equation for finding the average speed.
 Average speed= total distance/total time
 Problem: Imagine that two birds leave the same tree at
the same time. They both fly at 10km/h for 10min.
Why don’t they end up at the same place?
 A: The birds went in different directions. Their speeds
were the same but they had different VELOCITIES.
 Velocity: the speed of an object IN A PARTICULAR
DIRECTION.
 Do not confuse the terms speed and velocity.
 Velocity must include a reference direction
 Ex. The speed of the car is 54 mph.
 Ex. The velocity of the car is 54 mph east.
 Think of velocity as “the rate of change of an object’s
position.”
 An object’s velocity is constant only if its speed and
direction don’t change. Therefore, constant velocity is
always motion along a straight line.
 Velocity can change if an object’s speed or direction
changes.
 Weather changes vel.
 Imagine that you are riding on a bus that is traveling east
at 15 m/s. You and the other passengers are also traveling at
a velocity of 15 m/s east. But suppose you stand up and
walk down the bus’s aisle while the bus is moving. Are you
still moving at the same velocity as the bus?
 Resultant velocity: when you combine two velocities.
 To find resultant velocity:
 If velocities are going in the same direction, add them
together.
 If the velocities are going in opposite directions, subtract the
smaller velocity from the larger velocity. The resultant
velocity is in the direction of the larger velocity.
 Although the word accelerate is commonly used to mean
“speed up” the word means something else in science.
 Acceleration: the rate at which velocity changes.
 An object accelerates if its speed, direction or both change.
 An increase in velocity is commonly called “positive
acceleration.”
 A decrease in velocity is commonly called “negative
acceleration” or “deceleration.”
 Keep in mind that acceleration is not only HOW MUCH
velocity changes but also HOW FAST velocity changes.
The faster the velocity changes, the greater the acceleration
is.
 You are riding your bike at 9km/h. Ten minutes later,
your speed is 6km/h.
 You ride your bike around the block at a constant
speed of 11km/h.
 You ride your bike in a straight line at a constant speed
of 10km/h.
 To find average acceleration use the following
equation:
 Average acceleration = Final velocity-Starting velocity/
time it takes to change velocity.
 Velocity is expressed in meters per second (m/s) and
time is expressed in seconds (s). So acceleration is
expressed in (m/s)/s which equals m/s squared.
 Imagine this were a roller coaster. How would you
interpret the acceleration of the rollercoaster
according to the lines on this graph?
 Even when you are completely still you are
experiencing acceleration.
 You are traveling in a circle as the earth rotates.
 An object traveling in a circular motion is always
changing its direction. Therefore, its velocity is always
changing, so it is accelerating.
 Centripetal Acceleration: acceleration that occurs in
circular motion.