1. Forces & Motion Review
(material so far)
2. Gravity
Mrs. Deeley
7th Grade Science
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IMPORTANT: On each slide,
click on the speaker at the top
right of the slide to hear your
lecture notes. Be sure your
sound is turned up.
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Click on speaker
Review
Motion is a change in position over time.
Motion is described in relation to a reference point.
Speed is the rate of motion.
Inertia is the tendency of an object to resist having its motion changed.
Mass of an object influences it motion.
Forces acting on an object can be balanced or unbalanced.
Many forces may be acting on an object. Examples of forces include gravity,
magnets, friction, and contact.
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Source: Gravity Movie
Isaac Newton
Source: CK12
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Gravity is a Universal Force
• Newton’s law of gravity is called the law of universal gravitation.
• Universal gravitation means that the force that causes an apple to fall from a
tree to the ground is the same force that causes the moon to keep moving
around Earth.
• Universal gravitation also means that while Earth exerts a pull on you, you
exert a pull on Earth. In fact, there is gravity between you and every mass
around you—your desk, your book, your pen. Even tiny molecules of gas are
attracted to one another by the force of gravity.
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Gravity
• Gravity is the force that objects exert on each other because of their masses.
• Mass: a measure of how much matter an object is made of.
• Matter: Anything that has mass and volume. Matter is typically a solid, liquid, or a gas.
• When you drop any object (for example, a pencil), it falls to the ground. As
the object falls, it moves faster and faster.
• The downward pull of an object is due to gravity.
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Gravity, Mass, and Distance
Mass
• The more mass two objects have, the greater the force of gravity the masses exert
on each other.
• If one of the masses is doubled, the force of gravity between the objects is doubled.
• Greater mass results in greater force.
Distance
• As distance between objects increases, the force of gravity decreases.
• If the distance is doubled, the force of gravity is one-fourth as strong as before.
• Greater distance results in smaller force.
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Question
• Which has more gravitational attraction, a pair of students standing one
meter apart or the same students standing three meters apart? Explain your
answer.
Sentence starter: When the students are standing _______________ meters
apart, there is more gravitational attraction because ____________________
____________________________________________________________.
**Be sure and include these terms in your answer: mass, distance, force, gravity
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Gravity on Earth
• The force of gravity acts on all objects; however, the effects on the objects
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can be different depending on their mass.
Objects with more mass: gravity exerts more force on it.
The greater the mass of an object, the more inertia so the greater force does not
produce a larger acceleration. Recall: inertia is the tendency of an object to resist a
change in motion.
Objects with different masses fall with the same acceleration.
The acceleration due to Earth’s gravity is called g and is equal to 9.8 m/s2 (meters
per second squared) at Earth’s surface.
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Summary
• Newton’s law of universal gravitation states that the force of gravity affects
everything with mass in the universe.
• Newton’s law also states that the strength of gravity between any two objects
depends on the masses of the objects and the distance between them.
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References
1. McDougal Littell Science
2. CK12 Flexbooks
3. Gravity Movie
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