Was Galileo Wrong Galileo dropped two objects off a tower Try dropping a book and a sheet of paper Do they hit the ground at the same time They don’t Was Galileo wrong Not at all A sheet of paper has more air resistance That slows its fall Heavy objects are not as affected by air resistance as light ones Do the experiment in a vacuum where there’s no air They’ll hit the ground at the same time place the paper on top of the book Let go Do they fall at the same rate The book removes the air resistance They should hit the ground at the same time Try the experiment again This time 6
Sir Isaac Newton studied nature in the late 1600s He wondered why the Moon moved and never fell because he knew that when ordinary objects fell they always hit the ground Newton believed the same force that pulled objects down might be the same force that pulled the Moon He defined this force as gravity the unseen force holding the universe together Newton’s laws of motion and gravity came from his interest in the Moon Newton said all objects have mass Mass is the amount of matter in something Mass stays the same Everything with mass exerts or applies a force on every other thing Small masses exert less force so the force isn't as noticeable Isaac Newton 1643-1727 7
Mass is different from weight Weight is defined as the force of attraction between a person and place in the universe Weight can change depending on the location On Earth a person has a set amount of mass Their weight is in pounds or kilograms and will change if they leave Earth On the Moon that same person has the same mass but their weight is less The smaller-sized Moon exerts less gravitational pull on their mass The Moon’s mass is less so its gravitational pull is less more mass a body has a stronger pull Gravity exists between any two objects in the universe With What Would You Weigh on Other Objects in Space Ever wonder what you might weigh on Mars or the Moon Here's your chance to find out If you weigh approximately 100 pounds 45 5 kilograms on Earth this is what you would weigh on different objects in space 8 MOON THE SUN YOUR WEIGHT IS 16 lb 7 3 kg YOUR WEIGHT IS 2,707 lb 1,230 5 kg EARTH MARS YOUR WEIGHT IS 100 lb 45 5 kg YOUR WEIGHT IS 38 lb 17 3 kg
Planets with large masses have a strong gravitational pull The force a person exerts on a planet is small A planet’s huge mass holds people to the ground Distant bodies exert less gravitational pull The Sun is too distant to pull people to it Smaller bodies exert less pull That’s why people don’t fall toward other people Newton’s ideas introduced the science of mechanics Mechanics is the study of forces and motion The same force that pulls things toward Earth also pulls on things out in space The Moon would go off in a straight line without Earth’s gravity MERCURY VENUS YOUR WEIGHT IS 38 lb 17 3 kg YOUR WEIGHT IS 91 lb 41 4 kg Units Used to Measure Weight lb Pounds kg Kilograms JUPITER SATURN URANUS NEPTUNE PLUTO YOUR WEIGHT IS 236 lb 107 3 kg YOUR WEIGHT IS 106 lb 48 2 kg YOUR WEIGHT IS 89 lb 40 5 kg YOUR WEIGHT IS 113 lb 51 4 kg YOUR WEIGHT IS 7 lb 3 2 kg 9
