Introduction to In Motion

Part 2

Review

In previous learning we have looked at the differences between different vocabulary words in physics. Most notably:

Scalar vs. VectorDistance Vs. Displacement

Comparing Again...

Two words that have meanings that can be very similar are :

SPEED andVELOCITY

What’s the fastest human speed? (2 videos)

SPEED

How fast an object is moving Think of when we learned about distance,

all we are doing is adding how much time it took to cover that distance.

A scalar, therefore there is no direction of motion.

Examples...▪ 20 km/hr▪ 40 m/s▪ 1 mm/ms

FORMULA FOR SPEED

Speed in measured in 2 quantities:▪ How fast an object is going in time (ex 10

km/hr)

In order to calculate speed in this time, we simply take the distance value (such as km or m) and divide it by the time value (such as hours or seconds).

FORMULA FOR SPEED

SPEED = distance

time

Ticker Tape Example

Faster vs. Slower When will the points be closer

together? When the tape is pulled faster or when the tape is pulled slower?

Why is this?

Student Examples.

In groups of 2, grab a stop watch. Decide on a set amount of distance,

such as 10 steps or from one end of the room to another.

Have 1 person cover the distance, while the other person times how long it takes.

Reverse roles. Try out your calculations and

determine who has the fastest speed.

Speed Calculation Examples

Try out the following examples:1) A car travels 140 km in a 2 hour

time. What is its speed in km/hr?2) A person Sam walks to school a

total distance of 9.8 km. It takes him about 3.5 hours. What is his speed in km/hr?

3) A duck ran .03 km in .010 hours. What is its speed in km/hr?

VELOCITY

How fast an object’s position is changing. Rate of change of position. Think of when we learned about displacement,

all we are doing is adding how much time it took to change the postion of the person .

Vector quantity, with both speed and direction. Change in distance in change in time

Example:▪ 140 m W in 10 seconds

FORMULA FOR VELOCITY

Velocity = the change in distance (or amount)

the change in time (or amount)

‘Change in’ can also be written as ∆ (delta). av

dV

t

FORMULA FOR VELOCITY

VELOCITY = DISPLACEMENT

CHANGE IN TIME

Change in Distance (Displacement)

In order to move an object, we must change the object’s position. Any change in position is called displacement.

Along a straight line, change in distance can be found by the final position minus the initial position.

Or ∆d = position 2 (final) – position 1

Or ∆d = d₂ - d₁

The number line

Example: A car moves across a table in a straight line. The initial position of the car is -1 cm. If the car stops at the +3 mark, calculate the displacement of the car.

Displacement another way...

-Calculate the displacement of each object:- CAR =

-BICYCLE =

-PEDESTRIAN =

-SKATEBOARDER=

Student Examples.

In groups of 2, grab a stop watch. Decide on a set amount of

displacement, such as 10 steps from your seat or a lap around the room..

Have 1 person cover the displacement, while the other person times how long it takes.

Reverse roles. Try out your calculations and determine

who has the fastest speed.

Displacement in direction

When dealing with compass direction (North, East, South and West) you must also qualify the directions as either positive or negative. +

+

-

-

Calculating the Change in time An Interval of time or change in time. How much time was used. Most questions will give you a set amount

of time.▪ Example: Traveled for 3 hours = TOTAL TIME = 3

hours

However, if the question has more than 1 time value, you simply add them together▪ Example traveled for 2 hours then 1 hour = TOTAL

TIME = 3 hours

Practice Problems

Speed vs. Velocity

13 questions total, we will go through 1 and 2 together first.