"Exploration - Comparing the Speed ​​of Movement of Objects" Simple Movement of Matter PPT Courseware 2

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"Exploration - Comparing the Speed ​​of Movement of Objects" Simple Movement of Matter PPT Courseware 2

We learned that knowledge together yesterday

Mechanical motion Change in position of an object

Reference object To say whether an object is moving or stationary depends on which object is used as the standard.

The relativity of motion and rest

How to move?

The world is in motion, and motion comes in many forms.

Different objects move at different speeds

Objects can move fast or slowly. What methods can describe the speed of an object's movement?

1. In the story of the tortoise and the hare, what is the basis for judging the victory of the tortoise?

2. What criteria are used to determine the champion in the 100-meter dash?

3. Among the cars and bicycles driving on the road, which one moves faster? And on what basis?

1. Methods to compare the speed of movement of objects:

1. Same distance than time (100-meter race)

2. Same time than distance (the tortoise and the hare)

2. Speed

(1) Physical meaning and definition:

Meaning: A physical quantity that expresses the speed of an object's movement.

Definition: The distance traveled by a moving object in unit time.

(2) Formula: v=s/t

s—distance—meter (m)

t—time—second (s)

v—speed—meters per second (m/s)

Example 1 Liu Xiang, an outstanding Chinese athlete, won the gold medal in the 110m hurdles at the 2004 Athens Olympics with a time of 12.91s. What was the speed of this Olympic record? If the speedometer of a moving motorcycle indicates 30km/h. Which one has greater speed?

Solution: Using the formula v=s/t, Liu Xiang’s speed can be calculated as:

During the problem-solving process, you need to write down the formulas you use. When substituting values ​​and units, the units must be unified. The result is in units.

Example 2 After the train speed is increased, the operating speed between Beijing and Shanghai is 104km/h. The railway line length between the two places is 1463km. How long does it take the train from Beijing to Shanghai?

Solution: By deforming the formula v = s/t, we can get t = s/v,

Therefore, the time it takes for a train to travel from Beijing to Shanghai is approximately

t = s/v =1463km/(104km/h)=14h

Practice in time: The scientific name of China's "bullet" train is "EMU". As shown in the figure, this new type of train uses the latest locomotive technology in terms of power, materials and internal structure. The CRH-Z electric multiple unit put into use has a maximum speed of 250km/h. Take Beijing-Shanghai as an example , starting from Beijing at 9:36 and arriving in Shanghai at 16:36, the whole journey is 1463km, then the average speed of this EMU is _______km/h.

2. Uniform linear motion

The motion of an object along a straight line with constant speed is called uniform linear motion.

Uniform linear motion is the simplest mechanical motion.

Variable speed linear motion: linear motion in which the speed changes frequently.

Common sports are variable speed sports.

When an object moves at variable speeds, its speed is sometimes fast and sometimes slow. How to describe its movement?

Variable speed movement is relatively complicated. If you just do a rough study,

You can also use the formula v=s/t=total distance/total time to calculate its speed. The speed calculated in this way is called the average speed.

Summary

1. Speed ​​is a physical quantity that expresses how fast an object moves.

In uniform linear motion, the speed is equal to the distance traveled by the moving object in unit time.

The formula for calculating the speed of uniform linear motion is v=s/t

The units of speed are meters per second (m/s) and kilometers per hour (km/h). 1 m/s = 3.6 km/h

2. In variable speed motion, v=s/t to find the average speed.

Consolidation exercises

1. Unit conversion:

10m/s=_____km/h

54km/h=____m/s

2. Which of the following speeds is the largest ( )

A.750m/min B.15m/s

C.36km/h D.1250cm/s

3. A passenger sitting in a moving car wants to estimate the length of the tunnel ahead. When entering and leaving the tunnel entrance, I looked at my watch respectively. As shown in Figures (A) and (B), the average speed of the car when passing through the tunnel is 30 km/h. From this, it can be calculated that the length of the tunnel is approximately _______km.

4. A train is 200m long and passes through a 1.6km long bridge at a speed of 36km/h. How long does it take for the trains to arrive on the bridge and leave the bridge?

Solution: The distance the train passes from entering the bridge to completely leaving the bridge is s=1.6km+0.2km=1.8km

The speed of the train is v = 36 km/h

t = s/v =1.8km/36km/h=0.05h

Answer: The time it takes for all trains to leave the bridge is 0.05h.

Compliance self-test

1. Speed ​​is a physical quantity used to represent the ______ of an object.

2. An object moving in a straight line at a uniform speed covers a distance of 120m in 1 minute. Its speed is _____ m/s, and its physical meaning is _______.

3. An object moving in a straight line at a uniform speed travels 20m in 4 seconds, so its speed in the first 2 seconds must be ( )

A.80m/s B.10 m/s C.5 m/s D.Unable to determine

4. Regarding the speed formula v=s/t for uniform linear motion, which of the following statements is correct ( )

A. The greater the speed v of the object, the longer the distance s traveled.

B. The greater the speed v of the object, the less time t it takes

C. The speed of an object’s movement is directly proportional to the distance and inversely proportional to time.

D. The object v is determined by s/t, but has nothing to do with the size of s and t.

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"Exploration - Comparing the Speed ​​of Movement of Objects" Simple Movement of Matter PPT Courseware 6:

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"Exploration - Comparing the Speed ​​of Movement of Objects" Simple Movement of Matter PPT Courseware 5:

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"Exploration - Comparing the Speed ​​of Movement of Objects" Simple Movement of Matter PPT Courseware 4:

"Exploring and Comparing the Speed ​​of Movement of Objects" Simple Movement of Matter PPT Courseware 4 Question 1 In a 100-meter race, athlete A completes the distance in 10 seconds, and athlete B completes the distance in 11 seconds. Which athlete runs faster? Question 2: Car A travels 80km in 2 hours, and Car B...

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Update Time: 2024-10-02

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