"Measuring Average Speed" Mechanical Motion PPT Download

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"Measuring Average Speed" Mechanical Motion PPT Download

The first part: sorting out new knowledge

1. Measuring the average speed of an object’s movement

1. Ask a question: When the car slides down the slope, does the speed change? How?

2. Conjecture and hypothesis: The speed of the car may be increasing while sliding down the slope.

3. Design experiments and conduct experiments

Purpose of the experiment: Learn to use a scale and a stopwatch to measure the average speed of a car; practice using a scale and a stopwatch.

Experimental principle: _______.

Experimental equipment: long wooden boards, small wooden blocks, carts, metal sheets, ______, ______.

Experimental steps:

(1) As shown in Figure 1-4-1, pad one end of the long wooden board with a small wooden block to keep it at a small slope.

(2) Place the car on the top of the slope and the metal piece on the bottom of the slope. Use a scale to measure the distance s1 that the car will pass through. Fill s1 and the subsequent measured data into the experimental data recording form.

(3) Use a stopwatch to measure the time t1 from when the car slides down from the top of the slope to hitting the metal sheet.

(4) Based on the measured s1 and t1, use the formula ______ to calculate the average speed v1 of the car throughout the entire journey through the slope. distance s2.

(5) Move the metal piece to the middle of the slope and measure the distance s2 from the car to the metal piece.

(6) Measure the time t2 it takes for the car to slide from the top of the slope through the upper half of the slope s2, and calculate the average speed v2 of the car through the upper half of the slope.

(7) The second half of the journey s3 = __________, the time it takes the car to pass the second half of the journey t3 = __________, from which the average speed v3 of the car through the second half of the journey is calculated.

4. Data recording table

5. Analytical argument: Find v2___________ (optional "greater than", "less than" or "equal to") v3 through calculation. This shows that the speed of the car's descent gradually _________(optional "increase", "decrease" or "unchanged").

6. Evaluation communication:

(1) During the experiment, the slope of the incline should be _____________ (optional "bigger", "smaller" or "any size is OK"), in order to facilitate accurate measurement_______________.

(2) When measuring the distance traveled by a car, you must measure from the front (rear) of the car when timing starts to the front (rear) of the car when timing ends. You cannot measure from the top of the slope to the bottom of the slope or from the front to the rear of the car.

① When measuring the distance traveled by a car, if you measure from the front of the car when timing starts to the rear of the car when timing ends, the measurement result will be ______ (optional "too large", "too small" or "unchanged").

② When measuring the distance traveled by the car, if the measurement is from the rear of the car when timing starts to the front of the car when timing ends, the measurement result will be _______ (optional "too large", "too small" or "unchanged").

Measuring average speed PPT, part 2: application examples

Type 1: Measuring the average speed of an object

Example 1 2018·Hengyang measures the average speed of the car on the inclined plane as shown in Figure 1-4-2. Let the car start to slide down from stationary point A on the inclined plane, and measure the time it takes for the car to reach points B and C respectively. The average speed at different stages can be measured. For this experiment, the correct data processing is ()

A. The distance of section AB in the figure is sAB=50.0 cm

B. If the measured time for the car to pass through the AC section is tAC=2.5 s, then the average speed of the AC section vAC=32 cm/s

C. When measuring the time for the car to reach point B, if the car stops timing after passing point B, the measured average speed vAB of section AB will be too large.

D. In order to measure the average speed vBC of the car in section BC, the car can be released from stationary at point B.

Type 2 Ultrasonic ranging

Example 2: In shipwreck salvage, echolocators are used to locate sunken ships and measure sea depth. Its working principle is to emit sound waves into the sea, receive echo signals, and calculate and display the measurement results through the central processor. A certain time, ultrasonic waves were emitted vertically to the seafloor, and the returned signal was received after 4 seconds. The depth at that point in the ocean was ________m. (The speed of sound waves in sea water is 1500 m/s)

Measuring average speed PPT, Part 3: Class feedback

1. To study the changes in the speed of an object during motion, it is necessary to measure the ________ the object passes through each section and the ________ it takes to travel through each section, and use the formula ________ to calculate the average speed of the object in each section.

2. In order to explore "the change in speed of the car when it slides down the slope", a device as shown in Figure 4-1 is provided for you.

(1) To complete this exploratory experiment, the measuring tools required are ________ and ________.

(2)The principle based on the experiment is ____________.

(3) If each grid of the stop table in the figure represents 1 s, then in the experiment, the average speed of the car through the first half of the distance is ________m/s, and the average speed of the car through the whole distance is ________m/s.

(4) When the car slides down the slope, the change in speed is _______________.

3． The distance between A and B is 900 km. A train departs from A to B at 7:30 in the morning, stops at several stations on the way, and arrives at B at 16:30 that day. The train passes through a bridge with a length of 400 m at a constant speed of 144 km/h. The time for the entire train to pass the bridge is 25 s. beg:

(1) What is the average speed of the train from point A to point B in kilometers per hour.

(2)How many meters is the length of the train?

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Update Time: 2024-10-07

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