Measuring Motion

Determining if an object is in motion and how it is moving, isn’t as simple as it sounds: The concept of motion only makes sense when we have a reference point, or something to compare it to. We say a paper airplane thrown across a room is in motion only because we compare it to ourselves and other stationary, or fixed objects in the room like desks, floor tiles, etc.. In the very same way, the motion of clouds is perceived because they move over stationary objects like rooftops and our heads, or even move past the sun or the moon in the sky. But even the very objects that seem stationary or fixed in which we compare these moving objects to aren’t exactly stationary.....

Could you read the words in a book or magazine if it was moving at 500 mph? Of course not, right? Well, If you have ever flown anywhere you have done just that! But, the book doesn’t seem like its in motion, let alone moving at 500mph, because you are moving at the same speed as it is. But, if you have never flown in a jet you haven’t experienced the thrill of moving at such great speeds, right? Wrong! Everyone on the Earth moves at 1000mph each day, everyday, all day! You cover 24,000 miles in only 24 hours! You don’t notice this though, because everything around you – your dog, your Twinkie, even the air is moving at the same speed as you.

Our galaxy moves through space at the rate 1,340,000mph Even though we know the Earth spins on it’s axis, surely our planet must stay in one spot....After all, astronauts don’t often return from a 2 week stay on the International Space Station only to find the Earth is missing – “not where they left it”! But, the Earth, to, does move very quickly. It moves completely around the sun – a 595 million mile round trip in only 365 days! The math anyone? = _______ mph 67,000 In this case, we are calculating the motion of the Earth in relationship to the sun. We are assuming that the sun is a stationary or a fixed point of reference – a faulty assumption..... The sun and it’s solar system (us) rotate around the Milky Way (our) Galaxy at 486,000 mph! Our galaxy moves through space at the rate 1,340,000mph The next time someone asks you how fast you’ve been, use this number. But don’t brag, because so have they!

Clearly, Motion is relative Clearly, Motion is relative. It only makes sense when we use a common Reference Point. This concept is important to keep in mind when dealing with all of the characteristics of motion we will come across, Such as: Determining Speed takes only two variables into consideration – Distance and Time. Dividing distance covered by time elapsed will give you the speed of an object! SPEED Example: Let’s say you run a 600 meter race in 1 minute. What is your Speed then? You have the 2 things needed to calculate speed – a distance and a time. Distance 600 m Speed = Speed = Time 60 s Your speed would be 600 meters per 60 seconds, but should be simplified to a 1 second measurement. Thus, your speed would be 10 meters per second (10m/s). Additionally, if you know any 2 of the 3 variables, you can easily calculate the third: If you run at 6m/s, how long will it take you to run a 600m race? If you run at 6m/s, how far will you travel in 1 minute?

Exercises Kara entered a 50 meter swimming race at her school. She managed to complete the race in 25 seconds. What was Kara’s average speed for this race? Average speed = Total Distance Total Time Average speed = 50 meters = 2 m/s 25 seconds A Train is traveling at an average speed of 120 k/h. How long will it take the train to reach it’s next destination which is 480 kilometers away? 120 = 480 = 4hours ? Bonus! Howard wants to calculate the average speed in which his finger nails grow. After much waiting he measures the length after exactly 60 days. He reports that his fingernails grow at a speed of 1/25,000 of a millimeter per hour. How much did his nails grow? A. 3.6mm C. 2.3mm B. 4.1mm D. 5.5mm

Velocity – Speed in a given direction. Speed is not the same thing as Velocity. Velocity takes both speed and direction of motion into consideration. In order to determine velocity, we must know how fast it is going and in what direction – north, south, east, west, up, down, or anywhere in between. Velocity – Speed in a given direction. An Air Traffic Controller would be of little help if they only knew the speed of the jets they track. They must also know the direction and altitude of the jet to avoid collisions. This is VELOCITY! When there is a change in Velocity we call this Acceleration. Remember, in order to change velocity, there either has to be a change in __________ , __________ or both. Speed Direction Hints: When an object’s speed decreases, this is considered to be negative acceleration. A more common term for this is deceleration. A change in direction can result in both acceleration and deceleration!

Calculating “Average Acceleration” When you combine two velocities that are in the same direction, you ADD them together. When you combine two velocities that are in the opposite direction, you SUBTRACT the smaller number from the larger number. If you are walking from the back of a train to the front of a train, you would add your velocity to the train’s (same direction). If you were instead walking from the front of the train to the back of the train, you would subtract your velocity from the train’s (opposite direction) Example: Calculating “Average Acceleration” Average Acceleration = final velocity - starting velocity time it takes to change velocity Use this formula to find out your average acceleration in each of the following situations: A. You are jogging along at 3m/s going north but speed up to 5m/s when a bee chases you for 2 seconds. B. You are jogging along at 3m/s going south and in 1 second slow down to 1m/s to avoid a puddle. A. 1m/s² north (positive acceleration) B. -2 m/s² south (negative acceleration)