Mr. McMartin

Beta Pod Science

Measuring Motion

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.

Interesting Fact # 1

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.

Interesting Fact #2

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.

Interesting Fact #3

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.

Thing to Remember For Later…

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.”

Measuring Motion

The earth’s surfaceTrees BuildingsMoving objects in relation to one another.

Ex. If you were in a hot air balloon and you saw a bird fly buy.

Common Reference Points

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 kphFeet per second (ft/s) or fpsMiles per hour (mi/hr) or mph

Speed Depends on Distance & Time

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

Determining Average Speed

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.

Velocity: Direction Matters

Do not confuse the terms speed and velocity.Velocity must include a reference directionEx. The speed of the car is 54 mph. Ex. The velocity of the car is 54 mph east.

Velocity vs Speed

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.

Changing Velocity

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.

Combining velocities

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.

Acceleration

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.

Did Acceleration Occur? Why?

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.

Calculating Average Acceleration

Imagine this were a roller coaster. How would you interpret the acceleration of the rollercoaster according to the lines on this graph?

Acceleration on a 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.

Circular Motion: Continuous Acceleration