2. The measurement unit of shorter objects is usually centimeters, and the measurement unit of longer objects is usually meters.

3. Method of measuring the length of an object: align the left end of the object with the "0" scale of the ruler to see what the scale of the right end of the object is on the ruler. The length of this object is several centimeters.

4. Relationship between meter and centimeter: 1 meter = 100 cm 100 cm = 1 meter.

5. Line segment

Characteristics of (1) line segment:

① The line segment is straight;

② The line segment has two endpoints;

③ The length of the line segment can be measured.

⑵ Method of drawing line segments: first aim the pen at the `` 0' scale of the ruler, point a point on the top, then aim at the centimeter scale of the length to be drawn, point a point on the top, and then connect the two points.

(3) When measuring the length of an object, when the measurement is not started from the "0" scale, the scale number of the starting point should be subtracted from the scale number of the end point.

6. Fill in the appropriate length unit.

Xiaoming is 1 (m) 30 (cm) tall, his exercise book is 13 (cm) wide, and his pencil is 17 (cm).

Blackboard length 2 (m) Thumbnail length 1 (cm) A bed length 2 (m).

Jingshen 3 (meter) School Run 100 (meter) Competition. The teaching building is 25 meters high.

The baby is 80 (cm) tall, the skipping rope is 2 (m) long, and a tree is 3 (m) tall.

A key is 5 cm long, a pencil box is 24 cm long and the platform is 90 cm high.

The door is 2m high, the classroom is12m long and the chopsticks are 20cm long.