Topic: Forces and Motion
Aim: How does gravity act on objects?
Do Now: Take out your HW ditto.
http://www.brainpop.com/science/motionsforcesandtime/newtonslawsofmotion/
HW: Ditto – Newton’s Laws of Motion
1
2
3
4
•
Force
of
attraction
Gravity
between all objects in the
universe
Newton’s
Law of
Universal
Gravitation
• A force of gravity
acts between all
objects in the
universe.
• Gravity increases as mass
increases
• Gravity decreases as
distance increases
Weight
• Measure of the force
of gravity on an object
• W = mass x ag
–ag = 9.8
2
m/s
For every second an object falls,
its velocity increases by 9.8m/s
Suppose that an elephant and a
feather are dropped off a very
tall building from the same
height at the same time.
Suppose also that air resistance
could be eliminated such that
neither the elephant nor the
feather would experience any air
drag during the course of their
fall. Which object - the elephant
or the feather - will hit the
ground first? In the absence of
air resistance, the elephant and
the feather strike the ground at
the same time.
• Ex: How much does a 50kg
person weigh on Earth?
–W = m x a
–W = (50kg) (9.8 m/s2 )
–W = 490.0N
–(By the way, 4.55N = 1lb)
Let’s summarize…
1. Describe gravity.
2. State Newton’s law of universal gravitation.
3. Explain the relationship between gravity and mass.
4. Explain the relationship between gravity and
distance.
5. Describe weight.
6. State the formula that can be used to determine an
object’s weight.
7. What is the acceleration due to gravity?
http://www.brainpop.com/science/motionsforcesandtime/gravity/
http://www.youtube.com/watch?v=CfchR2EseD0
http://www.youtube.com/watch?v=gjfLI7aJKmQ
The moon has a smaller mass than the
earth. If you were able to travel to the
moon, your weight would
1. increase
2. decrease
3. remain the same
4. vary from day to night
The force of gravity on an object
depends primarily on the object’s
1. density
2. momentum
3. mass
4. volume
The distance of the star Vega from Earth is 1.6
million times greater than the distance from
the sun to the Earth. Which of the following
best describes the gravitational influence of
Vega on Earth?
1. It is roughly equal to that of the sun.
2. Its influence is greater than that of the sun.
3. Its influence is small because of its distance.
4. It influences the magnitude of Earth’s mass.
If a solid object is taken from Earth far
into space, which of the following
measurements of the object will
change the most?
1. density
2. mass
3. volume
4. weight
If you were able to go to the top of a
building and simultaneously drop an apple
and a basketball , they would hit the
ground at the same instant because
1. the force of gravity on them is equal
2. they have the same mass
3. air resistance on both is the same
4. they have the same amount of kinetic
energy
As a bike rider goes up a hill, the force of
gravity acts to
1. increase the weight of the rider
2. increase the acceleration of the rider
3. decrease the weight of the rider
4. decrease the speed of the rider
How would the measureable properties of a
golf ball change if it were moved from the
earth to the moon?
1. It would have the same weight but different
mass.
2. It would have the same mass but different
weight.
3. It would have the same density but
different mass.
4. It would have the same mass but different
density.
The moon orbits the earth at a speed of
approximately 1 kilometer per second. The
moon is kept in orbit by which of the
following?
1. Lunar phases
2. Magnetism
3. Gravity
4. Ocean tides
Which of the following cause a ship’s iron
anchor to sink to the ocean floor when
released overboard?
1. Nuclear forces
2. Magnetism
3. Gravity
4. Chemical forces
Which of the following statements best
describes the force of Earth’s gravity on a
rocket moving upwards?
1. The gravitational force is constant at all
altitudes.
2. The gravitational force is weaker when the
rocket is higher.
3. The gravitational force is stronger when
the rocket is higher.
4. The gravitational force is zero when the
altitude is greater than 10, 000 miles.
Which of the following statements
describes a result of Earth’s gravitational
force on the moon?
1. The Moon has craters.
2. The Moon orbits around the Earth.
3. The Moon lacks an atmosphere.
4. The Moon has less gravity than the
earth.