Question

1. what is a substance?
2. what is a mass?
3. what is a weight?
4. what is a model?
5. why do scientists use models?
6. list the seven si base units

a.
b.
c.
d.
e.
f.
g.

1. what is a second?
2. what is a meter?
3. what is a kilogram?

Explanation:

1. A substance is a form of matter with distinct chemical and physical properties.
2. Mass is a measure of the amount of matter in an object, an intrinsic property not dependent on location.
3. Weight is the force exerted on an object due to gravity, calculated as weight = mass × gravitational - acceleration.
4. A model is a representation of a system, concept, or object used to help understand, explain, or predict phenomena.
5. Scientists use models to simplify complex real - world systems, make predictions, test hypotheses, and communicate ideas.
6. The seven SI base units are: meter (length), kilogram (mass), second (time), ampere (electric current), kelvin (temperature), mole (amount of substance), candela (luminous intensity).
7. A second is the base unit of time in the SI system, defined as the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium - 133 atom.
8. A meter is the base unit of length in the SI system, defined as the distance traveled by light in a vacuum during a time interval of 1/299,792,458 of a second.
9. A kilogram is the base unit of mass in the SI system, defined by the International Prototype of the Kilogram (a platinum - iridium cylinder) until 2019, and now by a fundamental physical constant, the Planck constant.

Answer:

1. A form of matter with distinct properties.
2. Amount of matter in an object.
3. Force due to gravity (weight = mass × g).
4. Representation to aid understanding.
5. To simplify, predict, test, and communicate.
6. a. Meter (length)

b. Kilogram (mass)
c. Second (time)
d. Ampere (electric current)
e. Kelvin (temperature)
f. Mole (amount of substance)
g. Candela (luminous intensity)

1. Duration based on cesium - 133 atom radiation.
2. Distance light travels in a vacuum in a specific time.
3. Defined by the Planck constant (formerly by a prototype).