# Which is slowly becoming a unit of measurement

## Understanding Physics 2, Student Book

12 2  Workbook page 6–7 The mass of the body 1. How is the mass of a body shown? Bodies consist of a wide variety of materials ("substances"). But they all have two properties that are summarized under the term mass: a) Every body opposes a change in its speed or its direction of movement with a resistance (“every body wants to keep its movement”). This quality is called indolence. The greater the mass of a body, the greater its inertia. For example, it is more difficult to set it in motion or to divert it from its direction of movement. Where the coin stays ... (Fig.12.1) E1 Place a coin on a narrow strip of paper on the edge of the table. First pull the paper strip slowly, then jerkily. When you pull it slowly, the coin moves with the paper. When pulling jerkily, it remains on the table due to its inertia. Does the thread hold? (Fig.12.2) E1 Tie one thread each to a weight of 1 kg and 10 g. First slowly lift the two bodies, then jerk them up by the thread. When lifting jerkily, the different inertia of the two bodies becomes apparent. The thread breaks on the 1 kg piece. b) Between all bodies there is an attraction or gravitational force (lat. gravitas ... gravity). We feel this on earth as a weight force. 2. What unit of measurement do we use for the mass? In order to be able to compare the inertia and weight of bodies, we need a simple comparison body. Therefore, the mass of 1 dm 3 (= 1 l) of water at approx. + 4 ° C was established as the unit of measurement and called it 1 kilogram (1 kg). A metal cylinder made of platinum and iridium was produced for the precise determination of reference weights. This “original kilogram” is kept in Paris (Fig. 12.6). Driving off Braking Driver not wearing a seat belt 12.3 Behavior of a body when driving off and braking V1 12.1 Where the coin stays… V2 12.5 The mass of 1 kg corresponds roughly to the mass of 1 liter of water. 12.2 Does the thread hold? The mass of a body shows itself through its inertia and its weight. M 12.4 Comparison of the masses of different bodies 12.6 The international prototype of the kilogram (“original kilogram”) since 1889 The unit of mass m is 1 kilogram (1 kg). 1 kg mass corresponds roughly to the mass of 1 dm 3 (1 l) of water. M info box: 1 kg = 1,000 g (grams) 1 dag (decagram) = 10 g 1 t (ton) = 1,000 kg film u2uq7b For testing purposes only - property of the publisher öbv