MS-Speed & Velocity

Speed and Velocity

Learning Target: I can calculate the speed and velocity of an object.

MS-PS2-2 Plan an investigation to provide evidence that the change in an object’s motion depends on the sum of the forces on the object and the mass of the object.

Open Ended

What questions can we ask about this video?

An object’s position is its current distance and direction from a reference point.

A reference point is an object or place you use to describe the locations of other objects.

​Lets look at an example

Fill in the Blanks

What is the position of the red car using the black car as reference.

Open Ended

What would a negative and positive number indicate when describing an object's position?

​ Can anyone tell me what rate is?

How far the car moves in a given amount of time is an example of a rate.
A rate is an amount of something measured per unit of something else.

​Many rates describe changes or events that happen over time. Suppose that a man in an eating contest eats 60 hot dogs in 10 minutes.
Can you calculate the rate?

​Lets look at some examples

​However, not all rates involve time. A grocery store may sell watermelon at a rate of $0.70 per pound, which means that a 10-pound watermelon costs how much?

Speed

The rate that describes the distance an object moves over time is that object’s speed.. Speeds can be measured in various units, but all speeds are measured in units of distance per a unit of time. For example, a car’s speed is often measured in kilometers per hour (km/h) or miles per hour (mi/h or mph). Scientists often describe speeds using meters per second (m/s).

​Formula for Speed

​Distance
TIME

Open Ended

What do you notice about the rate of speed for each of the three balls shown in the image? Use the formula for calculations

The figure shows you how the same speed can be represented different ways. In 1 second, the bowling ball rolls 3 meters. In 2 seconds it rolls 6 meters, and in 4 seconds it rolls 12 meters. In all of these cases, its speed is 3 m/s.

Velocity

Speed is one way of describing how fast an object is going, but it does not tell you what direction the object is moving in.

Velocity is an object’s speed and direction of motion.

Open Ended

What is the difference in speed and velocity?

​Like speed, velocity can be measured in different units. Car velocity is usually expressed as kilometers per hour (km/h) in a given direction. You could describe velocity of a runner as 4 m/s toward the finish line, and the velocity of a snail is about 1.5 cm/min to the east.

​An object’s velocity can change from moment to moment. Instead of trying to calculate an object’s velocity at a given moment, you can calculate the object’s average velocity. You calculate the average velocity of an object by dividing the distance it traveled by time needed to travel that distance. To find the distance an object traveled, you subtract the object’s starting position from its ending position. So, the equation for average velocity is:

​the yellow car moves from −70 m to 20 m from the white line in 3 seconds. Additionally, the yellow car is moving in the positive direction along the number line to the east. Using the equation above, you can calculate its average velocity as:

​To fully describe the velocity of the car, you have to look at a situation to find and name the direction the car is going. Whether the velocity is positive or negative tells you if the object is moving forward or backward.

On the next slide you will work on example. Use the paper on your desk to work out the problem.

Fill in the Blanks

In the same amount of time, the red car moves from 50 m to −25 m from the white line in 3 seconds. It is moving in the negative direction to the west. Its average velocity is:

​Your answer should look like this. Notice that it contains the same units that were used in measuring the distance and time. Velocity also includes the direction.