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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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Forces & Motion Review. Describe Acceleration A change in velocity – which may be: –A change in speed Starting Stopping Speeding up Slowing down –A change.

Forces & Motion Review. Describe Acceleration A change in velocity – which may be: –A change in speed Starting Stopping Speeding up Slowing down –A change.

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