"Speed ​​and Slow of Movement" Mechanical Movement PPT Download

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"Speed ​​and Slow of Movement" Mechanical Movement PPT Download

The first part: sorting out new knowledge

1. Two ways to compare the speed of an object’s movement

[Dial]In nature, in most cases, the distance traveled by mechanically moving objects in different time periods is also different. We often use the "ratio of distance to time" to compare the speed of an object's movement. The essence is to "compare distances at the same time".

2. Speed ​​and its calculation

Physical meaning Speed ​​is a physical quantity that expresses the movement of an object ________

Definition In physics, the ratio of distance to time is called speed. Numerically equal to the _________ that an object passes through within ____________

formula

Unit Basic unit: Meter per second (m/s or m·s-1); Common unit: Kilometer per hour (km/h or km·h-1); Relationship: 1 m/s=3.6 km/h

3. Uniform linear motion

2. Uniform straight line motion: The motion of an object along _________ and _________ unchanged.

3． Variable speed linear motion: linear motion with changing speed, that is, the distance traveled by an object in equal time __________.

4. Average speed

1. Physical meaning: Used to roughly describe the average speed of an object moving at variable speeds. When expressing, be sure to indicate which section of the journey or average speed during which period of time.

2. Calculation: When calculating the average speed, the motion process under study must be clearly defined, and the average speed is calculated by dividing the total distance of this motion process by the total time. In the speed formula v=st, s must be the distance traveled within time t, and t must be the time it takes to pass distance s.

PPT on the speed of movement, part 2: application examples

Type 1 Comparison of the speed of object movement

Example 1: Figure 1-3-2 shows a scene of the 100-meter race at a school's track and field meet in 2019. The championship competition started between Wang Li and Li Juan. The game was coming to an end and when the contestants sprinted with all their strength, the audience saw the scene as shown in the picture and cheered "Wang Li is the fastest"; soon, based on the competition results shown in the table, the referee ruled that Wang Li had won. The audience and the referee The methods to judge whether Wang Li is faster than Li Juan are ()

A． Audience: Same time and distance. Referee: Same time and distance.

B. Audience: Same time compared to distance. Referee: Same distance compared to time.

C. Audience: Same distance compared to time. Referee: Same time compared to distance.

D. Audience: same distance compared to time. Referee: same distance compared to time.

[Method Guidance]Use the control variable method to compare the speed of object movement

When comparing the speed of an object's movement, the key to analysis is to find which factor, distance or time, is the same, and then compare the speed of the object's movement by comparing the size of the other factor.

Type 2: Distinguishing between uniform linear motion and variable speed linear motion

Example 2: A car is moving in a straight line. The distance and time of movement are shown in Figure 1-3-4. Then the car ()

A． It may be uniform linear motion

B. It must be a variable speed linear motion

C. It must be a uniform linear motion

D. None of the above answers are correct

Error-prone warning The speed of an object has nothing to do with distance and time.

Type 3 Calculation of average speed

Example 3 Mr. Zhang drove from Guangzhou to Zhaoqing. The car drove at an average speed of 90 km/h for 0.5 hours to reach Sanshui. After resting for 0.5 hours, the car drove at an average speed of 80 km/h for 1 hour to reach Zhaoqing. Excuse me:

(1) What is the distance traveled by car from Guangzhou to Sanshui?

(2) What is the average speed of cars from Guangzhou to Zhaoqing?

[Error-prone warning] (1) When calculating the average speed, you must indicate which distance or period the average speed is, because the average speed may be different at different times or distances. (2) The average speed is not the arithmetic mean of the speed, and the average speed of the whole process is not the arithmetic mean of the average speed of each section.

Type 4 Speed ​​Image Problem

Example 4 During extracurricular activities, Xiao Ming and Xiao Hua were both running and training along a straight track on the playground. In a certain training, the distance they passed changed with time as shown in Figure 1-3-4. Then the following statement is correct yes()

A． Both of them move in a straight line with uniform speed

B. Neither of them moves in a straight line at a uniform speed.

C. In the first 2 seconds, Xiaohua ran fast

D. Throughout the whole process, Xiaohua’s average speed was greater than Xiaoming’s average speed.

[ Analysis The image is a curve, which shows that distance is not proportional to time, so Xiaohua is not moving in a straight line at a uniform speed, so A and B are wrong. It can be seen from the image that in the first 2 s, Xiaohua moved longer than Xiaoming, so Xiaohua ran faster, so C is correct. It can be seen from the image that the distance traveled by the two people is equal, the time taken is 8 s, and the average speed of the two people is the same, so D is wrong.

PPT on the speed of exercise, part 3: Class feedback A

1. In life, people usually use two methods to compare the speed of exercise. Method ①: Same distance and time; Method ②: ____________________. Physics uses speed to describe the speed of motion, and the formula is v=st. This method is the same as the daily method ________ (optional "①" or "②"). Commonly used speed units are m/s and km/h, and the relationship is 1 m/s = ________km/h.

2. Speed ​​is a physical quantity that represents the _____________ of an object. In physics, ______________ is called speed, and its calculation formula is ______________. In the International System of Units, the basic unit of speed is _________, the symbol is _____________, 1 m/s=________km/h.

3． Complete the following unit conversions:

(1)72 km/h＝__________m/s.

(2)15 m/s=__________km/h.

4. Xiaomeng rides a bicycle from home for 12 minutes at a speed of 5 m/s to reach the high school entrance examination test center. Xiaomeng’s home is ________km from the test center.

PPT on the speed of exercise, part 4: Class feedback B

1. In physics, the motion of an object along ________ with speed ________ is called uniform linear motion. The distance traveled by an object moving in a straight line at a uniform speed in any equal time is ________, that is, the distance traveled is proportional to time.

2. Photograph the ball moving from left to right and expose it every equal time. The resulting photo is shown in Figure 3-1. Among them, the ball moving in a straight line at a uniform speed is ()

3． A car moves in a straight line at a constant speed on the road. The correct relationship between the distance s traveled by the car and the time t taken is ()

[ Analysis

4. Xiao Ming's home is 600 m away from the school. It takes him 10 minutes to walk to the school. Then his average walking speed is ()

A． 60m/sB. 6m/sC. 1 m/sD. 1 m/min

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Update Time: 2024-10-02

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