Hours are a unit of measurement used to track the passage of time. They are part of the 24-hour time system, which divides a day into 24 hours. Understanding hours is important for telling time, scheduling activities, and calculating time durations.

An hour is equal to 60 minutes or 3,600 seconds. It is denoted using the symbol "h". There are 24 hours in a day, and they are typically counted from 12:00 AM (midnight) to 11:59 PM.

On an analog clock, the hour hand makes one full revolution every 12 hours. Each hour is marked by a number from 1 to 12. On a digital clock, the hours are displayed using numbers from 1 to 12, followed by "AM" (ante meridiem) for times in the morning and "PM" (post meridiem) for times in the afternoon and evening.

To convert hours to minutes, you can multiply the number of hours by 60. For example, 2 hours is equal to 2 * 60 = 120 minutes. To convert hours to seconds, you can multiply the number of hours by 3,600. For example, 3 hours is equal to 3 * 3,600 = 10,800 seconds.

**Example 1:** If it is 3:00 PM now, how many hours until 7:00 PM?

To find the number of hours, we subtract the current time from the target time: 7:00 PM - 3:00 PM = 4 hours

**Example 2:** How many minutes are there in 5 hours?

To convert hours to minutes, we multiply by 60: 5 hours * 60 minutes/hour = 300 minutes

Understanding hours is an essential skill for everyday timekeeping and time-related calculations.

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Measurement (NCTM)

Understand measurable attributes of objects and the units, systems, and processes of measurement.

Recognize the attributes of length, volume, weight, area, and time.

Understand how to measure using nonstandard and standard units.

Select an appropriate unit and tool for the attribute being measured.

Apply appropriate techniques, tools, and formulas to determine measurements.

Use tools to measure.

Grade 2 Curriculum Focal Points (NCTM)

Measurement: Developing an understanding of linear measurement and facility in measuring lengths

Children develop an understanding of the meaning and processes of measurement, including such underlying concepts as partitioning (the mental activity of slicing the length of an object into equal-sized units) and transitivity (e.g., if object A is longer than object B and object B is longer than object C, then object A is longer than object C). They understand linear measure as an iteration of units and use rulers and other measurement tools with that understanding. They understand the need for equal-length units, the use of standard units of measure (centimeter and inch), and the inverse relationship between the size of a unit and the number of units used in a particular measurement (i.e., children recognize that the smaller the unit, the more iterations they need to cover a given length).

Connections to the Grade 2 Focal Points (NCTM)

Geometry and Measurement: Children estimate, measure, and compute lengths as they solve problems involving data, space, and movement through space. By composing and decomposing two-dimensional shapes (intentionally substituting arrangements of smaller shapes for larger shapes or substituting larger shapes for many smaller shapes), they use geometric knowledge and spatial reasoning to develop foundations for understanding area, fractions, and proportions.