Gravity Depends on Mass
Aligned to MS-PS2-4 — Next Generation Science Standards.
What this lesson teaches
Gravity is an attractive force between any two objects that have mass, and the force is stronger when the masses are larger. It is always a pull, never a push.
Worked examples
Example 1
The Sun's enormous mass pulls Earth into orbit, and Earth pulls back on the Sun. Because the Moon has far less mass than Earth, its surface gravity is only about one-sixth as strong.
Example 2
Gravity never switches off with distance, it just gets weaker. The Sun still pulls on Neptune from 4.5 billion kilometers away.
Example 3
Weight and mass are different. Your mass is the same on the Moon; your weight is one-sixth, because weight is the force gravity applies to that mass.
Practice questions
- Observe planetary data and describe how a planet's mass relates to its gravitational pull.
- Construct an argument, using evidence, that gravity is always attractive and never repulsive.
- Explain why you would weigh less on the Moon than on Earth even though your mass is unchanged.
Watch the lesson
Every lesson comes with a video taught in English and Spanish — the same video the QR code in the printed workbook opens.
▶ Watch this lessonEn español
La Gravedad Depende de la Masa
La gravedad es una fuerza de atracción entre dos objetos cualesquiera que tengan masa, y la fuerza es más intensa cuando las masas son mayores. Siempre es un jalón, nunca un empujón.
Ejemplo 1: La enorme masa del Sol jala a la Tierra en su órbita, y la Tierra jala de regreso al Sol. Como la Luna tiene mucha menos masa que la Tierra, su gravedad en la superficie es solo cerca de un sexto de intensa.
Ejemplo 2: La gravedad nunca se apaga con la distancia, solo se debilita. El Sol sigue jalando a Neptuno desde 4,500 millones de kilómetros.
Ejemplo 3: El peso y la masa son distintos. Tu masa es la misma en la Luna; tu peso es un sexto, porque el peso es la fuerza que la gravedad aplica a esa masa.
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