"Fast and Slow" The World of Movement PPT Courseware 5

Description

"Fast and Slow" The World of Movement PPT Courseware 5

The movement of objects has speed

Who moves faster? ________

On what basis do you base your judgment? ___________

How to compare the speed of an object's motion

1. Compare the distance traveled at the same time

2. Compare the time taken for the same distance

The first method is commonly used in physics, and the same time is taken as unit time.

Use the distance traveled per unit time to compare the speed of an object's movement

The distance traveled by an object per unit time is equal to its speed

physical meaning

Used to express the speed of object movement

concept

Speed ​​is equal to the distance traveled by an object in unit time

formula

Speed=distance/time V=s/t

Variation S=vt t=s/v

unit

Derivation: V=s/t unit of speed = unit of distance/unit of time

Meters/second=m/s pronounced as: meters per second

Kilometer/h = Kilometer/hour Km/h pronounced as: Kilometer per hour

name:

Basic unit: m/s Common unit: Km/h

practise

Complete the following unit conversions

1. 15 m/s＝＿＿km/h

2. 72 km/h＝＿＿m/s

Example: It took Zhang San to run 100 meters in 17 seconds, while Li Si ran 165 meters in 25 seconds. Who ran faster, Zhang San or Li Si?

Known: s1 =100m, t1 =17s, t2 =25s, s2 =165m.

Find: v1, v2

Solution: V1＝s1/t1=100m/17s≈ 5.9m/s

V2＝s2/t2=165m/25s=6.6m/s

Because V2 > V1, Li Si runs faster.

Answer: Li Si runs faster

Things to note when using formulas:

1. When answering, you must know, seek, solve and answer.

2. When applying, speed, distance, and time must be for the same object.

3. The units of the three quantities of speed, distance and time must be unified: either use basic units or use common units.

Uniform linear motion: linear motion in which an object moves at a constant speed

In any equal period of time, the distance traveled is equal.

Variable speed linear motion: linear motion in which the speed of an object changes

When an object is in motion, its speed changes. We can use average speed to roughly represent the average speed of an object in a certain distance or within a certain period of time.

Class summary

1. Speed

1. The physical meaning of speed: indicates how fast an object moves.

2. The concept of speed: Speed ​​is equal to the distance traveled by an object in unit time.

3. The formula of speed: V=s/t (definition formula) S=vt, t=s/v (variant form)

4. Unit of speed: basic unit m/s, common unit km/h

1m/s=3.6km/h 1km/h=5/18m/s

5. Measurement of speed:

(1) From V=s/t, measure s and t, and find v.

(2) Measure directly with a measuring instrument.

2. Uniform linear motion and variable speed linear motion

A straight-line motion in which an object moves at a constant speed is called uniform straight-line motion.

The linear motion in which the speed of an object changes is called variable speed linear motion.

practise:

1. A car is moving forward at a constant speed on a straight road with a speed of 5m/s. Then 5m/s means _______________.

2. A small car drives from Hechuan to Chongqing with an average speed of 35km/h. Then 35km/h means _______________.

after class homework:

1. Textbook P28, Assignments 1 and 2.

2. After-school practical activities: Use the measuring tools around us to measure the speed of falling paper.

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Update Time: 2024-09-08

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