## Motion Notes

**Motion**

In order to understand motion you must first understand the concept of

In order to understand motion you must first understand the concept of

**frame of reference**

**(background or object used to compare a moving object to). If you were watching a soccer match and one of the players was moving the ball to the opponents goal, what would be your frame of reference for that motion? Well, some possible answers could be the goal(s), the markings on the field...**

**Motion**

**is a change in position and is measured in three categories: speed, velocity & acceleration.**

**Speed**

**is easy to remember if you would remember the speed limit say in front of the school. The posted speed in front of the school is 15 mph. Speed is the distance (miles) and object travels per unit of time (hrs). The formula is speed = distance / time or s=d/t.**

If a skateboarder is travels 20 meters down the street and covers that distance in 20 seconds their speed would be 1 meter/second. s= d/t= 20 meters/ 20 seconds= 20 m/s.

If a skateboarder is travels 20 meters down the street and covers that distance in 20 seconds their speed would be 1 meter/second. s= d/t= 20 meters/ 20 seconds= 20 m/s.

**Velocity**

**is closely tied to speed but it is different in that it contains the component of direction. The definition is speed with direction. Example: if you were traveling on I-64 headed toward Richmond doing the speed limit your velocity would be 65 mi/hr East. The 65 mi/hr is the speed part and East is the directional component. Velocity has direction and speed does not express that part.**

**Acceleration**

**is one step farther than the other two categories. The definition is a change in velocity or a change in speed or direction. Note that speeding up and slowing down aren't the only ways you can accelerate. If you change your direction as you travel you also accelerate. Technically, slowing down is called deceleration and is expressed as a negative number. Speeding up is expressed as a positive number.**

**The**

**equation**

**for accleration is: acceleration = final velocity - initial(starting)velocity / time or**

**a=vf-vi/t**

**.**

**Problem**

**: You are in a car traveling at 65 km/hr and another car pulls in front of you and you slow down to 45 km/hr in 2 seconds. What is your acceleration? reading back through the problem you see that your**

vi= 65 km/hr and your vf= 45 km/hr and t= 2seconds. Plugging that into the equation you have......

a= 45 km/hr - 65 km/hr / 2 seconds = -20 km/hr / 2 seconds = -10 km/hr/s Note that since you decelerated the value expressed is a negative number.

vi= 65 km/hr and your vf= 45 km/hr and t= 2seconds. Plugging that into the equation you have......

a= 45 km/hr - 65 km/hr / 2 seconds = -20 km/hr / 2 seconds = -10 km/hr/s Note that since you decelerated the value expressed is a negative number.

**Problem**

**2: You are waiting at a stop light and the light turns green and you speed up to 45 km/hr in 5 seconds, what is your acceleration?**

a = vf-vi/t = 45 km/hr- 0 km/hr / 5 seconds = 45 km/hr / 5 s = 9 km/hr/s Note that this is positive because you sped up. Also note that since you were stopped at the light your vi was 0.

a = vf-vi/t = 45 km/hr- 0 km/hr / 5 seconds = 45 km/hr / 5 s = 9 km/hr/s Note that this is positive because you sped up. Also note that since you were stopped at the light your vi was 0.

**Problem**

**3: If you are traveling on a ferris wheel, do you accelerate? Answer: YES, because though your speed is constant you are constantly changing your direction (anything other than a straight line is changing direction).**