Lighthouse Lab – Gravity and Sir Isaac Newton

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Non-contact Forces – Gravitational Force
Why does a ball fall to the ground when you drop it? Why do skydivers fall to the surface of the Earth when they leap from an airplane?

For an object to be in motion, like a skydiver falling to the Earth’s surface, one or more unbalanced forces must act on it. All objects have an invisible force that pulls on other objects. This force is called gravitational force, or gravity. A skydiver falls to the surface of the Earth due to the pull of the Earth’s gravity.

The strength of an object’s gravitational force depends on it mass. The gravitational force of objects with a small mass, such as a tennis ball, is too weak to observe. Compared to a tennis ball, the Earth has a much greater mass. The strong gravitational force of the Earth keeps everything on the Earth’s surface. The Sun’s gravity attracts the Earth and other planets in the solar system. It keeps the planets and other objects in the solar system in orbit around the Sun.

Gravitational force also depends on distance. The closer objects are to each other, the greater the gravitational force.

Mass vs Weight
In everyday language, we often use the terms mass and weight to describe how heavy something is. But in science, mass and weight have different meanings.

Mass is a measure of how much matter is in an object. Weight is a measure of the force of gravity pulling an object. On Earth, everything is pulled by the gravitational force of the Earth. So, both the mass and weight of an object does not change. The gravity on the Earth’s moon is about one-sixth that of the Earth. This means you would weigh one-sixth as much when on the surface of the moon. An object in deep space, where there is no observable gravity acting on it, would have the same mass as it does on Earth but would have no weight at all.

Sir Isaac Newton is considered one of the most important scientists in history. He made many discoveries and provided detailed explanations for the many scientific theories he proposed.

Newton’s work provided explanations about the force of gravity and the movement of the moon around the Earth and the planets around the Sun.

Much of our understanding of force and motion comes from Newton’s laws of motion – three laws that describe the relationship between the motion of objects and the forces acting on them.

The unit of measurement for force is newtons (N), named after Sir Isaac Newton. On Earth a one-kilogram mass exerts a force of 9.8 newtons. Use this to calculate your weight in newtons.