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ZingPath: Gravity and Motion

Free Fall

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Gravity and Motion

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Lesson Focus

Free Fall

Physical Science

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You will conduct experiments with freefalling spheres and manipulate three variables: mass of falling objects, gravitational acceleration, and height from which objects are released.

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Now You Know

After completing this tutorial, you will be able to complete the following:

  • Explain that when there is no air resistance, objects with different masses will fall at the same rate.
  • Successfully predict that on planets with greater forces of gravity, objects will fall faster.
  • Explain that the greater the height of the drop, the longer the time to fall.

Everything You'll Have Covered

The Activity Object opens by discussing Galileo's classic free fall experiment. Galileo Galilei was born in Pisa, Italy in 1564, and died in Tuscany, Italy in 1642. He considered entering the priesthood when he was a young man, but he decided instead to study medicine. While working toward his medical degree, he changed course and began to pursue mathematics. Galileo eventually taught geometry, mechanics, and astronomy at the University of Padua in Italy. Throughout his career, Galileo made many contributions to mathematics and science and has been called "the Father of Modern Science."

One of Galileo's contributions came when he climbed to the top of the Leaning Tower of Pisa around 1590 to drop two spheres of different masses, but similar density and shape, to the ground. He found that the two spheres hit the ground at the same time. Until then, it was commonly believed that heavy objects fall faster than light objects.

Not every pair of objects will fall at the same rate, though. If two items are dropped from the same height and one is much denser than the other, the denser one will hit the ground first. If Galileo had dropped a lead ball and a wadded piece of paper of the same size in his experiment, the lead ball (with greater density) would have hit the ground first. This is because the air resistance affects the paper ball more. Additionally, air resistance will slow falling objects that have a greater leading surface. If a man without a parachute and a man with a parachute (with greater air resistance) jump from a great height at the same time, the man without a parachute will hit the ground first.

The Activity Object allows students to do free fall experiments similar to Galileo's. However, experiments are conducted in a room in which all air has been removed to eliminate air resistance. Additionally, gravitational force can be changed. Students explore the affects of mass, gravitational acceleration, and height on falling objects. When there is no air resistance, objects with the same mass fall at the same rate. The greater the gravitational acceleration, the faster the object falls. When gravitational acceleration is constant, the greater the height of the drop, the longer it takes for objects to fall.

The following key vocabulary terms will be used throughout this Activity Object:

acceleration - a vector quantity expressing the change in velocity over time; increase of velocity (speed)

air resistance - friction between an object's leading surface and air molecules; also called drag as it slows a falling object

gravitational acceleration - acceleration due to gravity measured in meters per seconds squared (m/s)

gravitational force - the force of attraction between all objects in the universe

mass - the amount of matter in an object; common metric units are the gram (g) and kilogram (kg)

negative relationship - as the values of one of the variables increases, the values of the second variable also decreases; in math this is called an inverse relationship

no relationship - as the values of one of the variables increases, the values of the second variable do not follow a trend of either increasing or decreasing

positive relationship - as the values of one of the variables increase, the values of the second variable also increase; in math this is called a positive correlation

Tutorial Details

Approximate Time 20 Minutes
Pre-requisite Concepts Students should be familiar with force.
Course Physical Science
Type of Tutorial Experiment
Key Vocabulary acceleration, air resistance, constant