Forces and Gravity: The Science of Motion
Forces and Gravity: The Science of Motion
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Forces and Gravity: The Science of Motion
What do you already know about forces and gravity?
Learning Objective
At the end of the lesson you will be able to explain what forces are, describe how gravity works, and explain how mass and distance affect gravity.
What is a Force?
A force is a push or pull on an object. Forces can set objects into motion, stop them, or change their direction.
Contact vs. Noncontact Forces
Contact forces require touching, like pushing a door. Noncontact forces act at a distance, like gravity.
Balanced and Unbalanced Forces
Unbalanced Forces
Balanced Forces
Balanced forces are equal in size and opposite in direction. They keep objects still or moving at constant speed.
Unbalanced forces are unequal. They cause objects to start moving, stop, speed up, slow down, or change direction.
Forces All Around Us
We experience forces every day. Sitting, walking, or throwing a ball all involve forces acting on objects.
Measuring Forces
Forces are measured in newtons (N), named after Sir Isaac Newton. A newton measures how much push or pull is used.
Sir Isaac Newton
Sir Isaac Newton was a scientist who studied forces and gravity, helping us understand how objects move.
How Forces Change Motion
Forces can start, stop, speed up, slow down, or change the direction of an object's movement.
Read the Statements and Drag and Drop
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second
True
False
A force is a pull only
Balanced forces cause a change in motion
Friction is a contact force
Magnetism is a contact force
The Power of Gravity
Gravity is a noncontact force that pulls objects toward each other. Earth's gravity keeps us on the ground.
Gravity Everywhere
Every object with mass has gravity, from a pebble to a planet. But large objects, like the Earth or the Sun, have much stronger gravity.
Matter=Mass
More Mass=Stronger or More gravity
Everyday Examples of Forces
Which item has the weakest gravitational force?
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second
Leaf
Shoes
Car
Pear
Which item has the strongest gravitational force?
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second
Leaf
Shoes
Car
Pear
Mass vs. Weight
Mass is the amount of matter in an object; it never changes. Weight is the force of gravity pulling on mass.
Put these in order from strongest gravity to weakest.
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Distance Affects Gravity
The strength of gravity depends on how close two objects are. The farther away, the weaker the gravitational pull.
Who does gravity pull on more you or a Jet in the sky?
Would your mass be more on Earth or Mars?
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second
More on Earth
More on Mars
It would be the same
Answer D
Would your weight be more on Earth or Mars?
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second
More on Earth
More on Mars
It would be the same
Answer D
Gravitational force is stronger between what 2 objects?
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Earth and the Ozone Layer
Earth and the Weather Balloon
Earth and the Meteors
Earth and the Cumulonimbus Cloud
Gravity in Action
A dropped hammer and feather fall at the same speed in a vacuum, but air resistance slows down feathers and paper.
A scientist is planning to land a small robot on two different planets:
Planet A is very large and has a lot of mass.
Planet B is smaller and has less mass, but the robot would land much closer to its surface.
Using what you know about how mass and distance affect gravitational force, explain which planet will pull on the robot more strongly.
Write down 3 things you learned in this lesson.
Write down 2 things you want to know more about.
Ask 1 question about something you haven't quite understood yet.
