Kinematics What is Kinematics Kinematics is just a

Kinematics

What is Kinematics? Kinematics is just a fancy way of saying that we are going to study motion, without making it all that complicated. The actually definition of kinematics is: Kinematics: the study of motion Eventually we will discuss the causes for different types of motion (forces) but for now we are just concerned with the motion itself.

Recognizing Motion We like to say that an object is in motion when it is moving. The better scientific definition of motion is below: Motion – an object is in motion when its distance from another, stationary object is changing. The second object is called a reference point

Reference Point • Observe the situations below – The object on the left is the reference point – The object on the right is moving when compared to the reference point • And a second situation – Here the object on the right is NOT moving in reference to the second object but it is when referenced to the sides of the screen

Further Explanation • Think about riding the metro – When you are riding on the train and use the ground outside as a reference you are moving • Your position compared to an object outside of the train is changing – When you use the person sitting next to you as a reference point, you are not moving. • Your position compared to the person sitting next to you is not changing, no matter how fast the train is travelling

How do we measure motion? • Now that we know motion when we see it we can make measurements regarding it. – There are 5 components to motion • • • Distance Displacement Speed Velocity Acceleration

Distance vs. Displacement Distance – How far a object has travelled Displacement – How far an object is from its original position A good way to think of this difference is if I go for a two mile run. I leave my apartment and run for a mile, turn around and run back for a mile. The total distance that I ran was two miles. BUT, because I started and ended in the same place, my total displacement was zero.

Distance vs. Displacement • Distance will always be an absolute value • Displacement can be positive or negative depending on the direction traveled – Observe the following situation: -3 -2 -1 0 +1 +2 +3 – How far did the ball travel (distance)? Answer 8 units – How far did the ball end up from its initial position (displacement)? Answer -2 units

Distance vs. Displacement • In the picture to the right, which line represents the distance travelled and which represents the displacement? – Distance – black dotted line – Displacement – red line • Click here for a further simulation of the relationship between these two concepts

Measuring Distance and Displacement Both distance and displacement are measured in the SI unit of meters. Use appropriate tools to measure these distances ruler for small measurements meter stick for larger measurements Remember, when we talk about distance or displacement values that are large, we use kilometers

Calculating Distance and Displacement When calculating distance and displacement, it is best to draw a picture (graph paper is really useful for this). For example, if a runner starts at position S, and follows the arrows below, what is his total distance and displacement? S 7 m 2 m 1 m 4 m 1 m 1 m 10 meters Total distance = Answer 30 m Total displacement = Answer 0 m 4 m

One More Practice Problem A paperboy is busy deliver papers up and down Wilson St. He travels 5 km West, turns around and goes 7 km East, turns back around and goes 11 km West, and turns back around one more time and goes 3 km East. What is his total distance and displacement? Total Distance = 5 Answer km + 7 km + 11 km + 3 km = 26 km Total Displacement = -5 Answer km + 7 km - 11 km + 3 km = -6 km or 6 km West If you can do these two practice problems, you are on your way! Final Questions

Questions • The study of motion without worrying about the forces causing it is known as _____ kinematics Answer • What are 3 quantities associated with motion? 1. Distance 2. Displacement 3. Speed Answer 4. Velocity 5. Acceleration • When calculating how fast you are running around a track would you use your total distance or your total displacement? Why? You should use your distance otherwise your speed would be Answer zero because your displacement after a full lap is zero.

Remember to write out 2 -5 questions about the notes for class!!