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Published byMarshall Dorsey Modified over 5 years ago

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What is motion? Motion is the change in the position of an object. To describe the motion of an object we use terms like: Distance, displacement, speed, velocity and acceleration

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Distance vs. displacement What is distance? Distance is the total path travelled by an object. - Distance has magnitude (value) only. What is displacement? Displacement is the shortest distance between the start point and finish point with direction - Displacement has magnitude (value) and direction. - The SI unit for both distance and displacement is meter (m)

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Example: A car moves from point A to point B then to point C as shown in the opposite diagram. Find the distance and displacement travelled by the car Answer: Distance = 800 + 300 = 1100 m Displacement = 1100 m to right Distance vs. displacement A BC 800 m 300 m A B C 800 m 300 m

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Example: A horse runs from point A to point C then back to point B as shown in the opposite diagram. Find the distance and displacement travelled by the horse. Answer: Distance = 800 + 200 = 1000 m Displacement = 600 m to right Distance vs. displacement ABC 600 m 200 m A B C 600 m 200 m

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Example: A man moves from point A to point B then to point C and finally to point D as shown in the opposite diagram. Find the distance and displacement travelled by the man Answer: Distance = 50 + 30 + 50 = 130 m Displacement = 30 m to north Distance vs. displacement AB CD 50 m 30 m AB CD 50 m 30 m

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Speed What is speed? Speed is the travelled distance per unit time. - speed can be calculated by the formula: or - The SI unit of speed is meter per second (m/s). - Another unit for speed is (km/h).

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Speed - Formula of speed can be manipulated using: d s t where d = s x t or

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Speed Example: A horse runs a distance of 1200 m in 40 s with constant speed. Calculate the speed of the horse. Answer: Given: d = 1200 m t = 40 s s = ?

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Speed Example: A car travels with a constant speed of 20 m/s. How much distance the car will travel in 8 s? Answer: Given: s = 20 m/s t = 8 s d = ?

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Speed Example: How long will it take a man running with a constant speed of 8 m/s to travel a distance of 400 m? Answer: Given: s = 8 m/s d = 400 m t = ?

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Speed Example: what does it mean to say that the speed of plane is 80 m/s? Answer: It means that the plane flies a distance of 80 m every second.

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Distance-time graph Speed could be represented by graph called distance- time graph. In distance-time graph: distance is represented on the vertical axis and time is represented on horizontal axis Time (s) Distance (m)

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Distance-time graph Distance-time graph could have different shapes, two of them are: Time (s) Distance (m) Time (s) Distance (m)

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Distance-time graph When the distance-time graph has the opposite shape then it means that the object is: moving with constant speed (speed is not changing) The slope (steepness) of the of the line equals the speed. The steeper the line (more slope) the greater is the speed Time (s) Distance (m)

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Distance-time graph Example: The opposite graph represents the motion of two objects A and B. Which of the two objects have more speed. Explain why. Answer: Object A has more speed because the slope of its line is steeper (has more slope). Time (s) Distance (m) A B

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Distance-time graph When the distance-time graph has the opposite shape then it means that the object is: at rest, not moving, speed = 0 or slope = 0 Time (s) Distance (m)

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Average speed and instantaneous speed When an object is moving with changing speed (speed is not constant) then its motion is described by: 1- Average speed. 2- Instantaneous speed. Average speed is the total distance travelled divided by the total time of travel. Instantaneous speed is the speed at a given moment (point of time) In a moving car instantaneous speed could be determined from the speedometer

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Velocity Velocity is the speed of an object and its direction. Speed has magnitude (value) only. Velocity has magnitude (value) and direction. 5 m/s

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