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Measuring MOTION

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**You can tell that an object has moved when its __________ has changed.**

position

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**The object used for comparing another object to describe its position is called a…**

frame of reference

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**Describe Acceleration**

A change in velocity – which may be: A change in speed Starting Stopping Speeding up Slowing down A change in direction Acceleration is caused by unbalanced forces More

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**The distance an object moves in a certain amount of time is called _________.**

speed

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**Describe Speed A way to describe motion**

Average speed - Rate of motion calculated by dividing the distance traveled by the amount of time it takes to travel that distance Constant speed - Speed that does not change Instantaneous speed - Speed of an object at any given time

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**What is the formula for calculating speed?**

Speed is calculated by dividing distance by time –

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Calculate This Speed A football field is about 100 m long. If it takes a person 20 seconds to run its length, how fast was the football player running?

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**Remember to include the UNITS!!**

Calculate this Speed: A football field is about 100 m long. If it takes a person 20 seconds to run its length, how fast was the football player running? Speed = Distance ÷ Time Speed = 100 m ÷ 20 s Speed = 5m/s Remember to include the UNITS!!

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**A ______ graph can be used to show the change in an object’s speed over time.**

line

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**Understanding and interpreting Graphs**

Distance Time Graphs Understanding and interpreting Graphs

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Distance Time Graphs Describing a journey made by an object is not exciting if you just use words. As with much of science, graphs are more revealing. Plotting distance against time can tell you a lot about a journey. Let's look at the axes: Time always runs horizontally (the x-axis). The arrow shows the direction of time. The further to the right, the longer time from the start. Distance runs vertically (the y-axis). The higher up the graph we go, the further we are from the start.

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**Not moving? This is what it looks like…**

If something is not moving, a horizontal line is drawn on a distance-time graph. Time is increasing to the right, but its distance does not change. It is stationary.

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Moving…. If something is moving at a steady speed, it means we expect the same increase in distance in a given time: Time is increasing to the right, and distance is increasing steadily with time. It moves at a steady speed.

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**Constant or Steady Speed…**

If something is moving at a steady speed, it means we expect the same increase in distance in a given time: Time is increasing to the right, and distance is increasing steadily with time. It moves at a steady speed.

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**Can you describe what is going on here?**

For the first part of the journey shown by the graph below, the object moved at a steady (slow) speed. It then suddenly increased its speed, covering a much larger distance in the same time. This sort of motion is not very realistic, but is easy to understand. It also makes calculations easier!

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**What is the effect of line ‘Steepness’, A.K.A slope…**

Both the lines below show that each object moved the same distance, but the steeper yellow line got there before the other one: A steeper gradient indicates a larger distance moved in a given time. In other words, higher speed. Both lines are of constant gradient, so both speeds are constant.

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Speeding Up! The line below is curving upwards. This shows an increase in speed, since the gradient is getting steeper: In other words, in a given time, the distance the object moves is larger. It is accelerating.

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**There are three parts to the journey shown below:**

Moving at a steady speed, slowly Not moving for quite some time Moving again, but at higher speed In all the graphs so far, we have not seen any numbers - it's about time we did!

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**Calculate the speeds of different sections within a graph**

Stage 1: speed = distance / time = 100 m / 10 s = 10 m/s Stage 2: speed = distance / time = 50 m / 10 s = 5 m/s Stage 3: speed = distance / time = 150 m / 20 s = 7·5 m/s

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Motion Graphs Describing the motion of an object is occasionally hard to do with words. Sometimes graphs help make motion easier to picture and therefore.

Motion Graphs Describing the motion of an object is occasionally hard to do with words. Sometimes graphs help make motion easier to picture and therefore.

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