Physical Science 5-3: Gravity & Motion

​Physical Science 5-3: Gravity & Motion

Multiple Choice

What is the definition of a force?

• When there is no change in the object's motion

• the overall force acting on an object after all forces are combined

• a push or a pull that acts on an object

• Whenever an object accelerates

Multiple Choice

What is the magnitude and direction of the force in the diagram shown?

• 70 N right

• 70 N left

• 50 N right

• 50 N left

Multiple Choice

Which of the following Forces is an example of a Contact Force?

• Friction

• Gravitational

• Electric

• Magnetic

Multiple Choice

Calculate the Net Force.

• 60N, Left

• 40N, Right

• 0N

• 60N, Right

​Lesson Objectives

• Define Gravity

• Differentiate between weight & Mass

• Describe how gravity affects objects

• Show how air resistance affects falling objects

• Define Free Fall

• Explain the path shown by a horizontally thrown path

​How Does Gravity Affect Matter

• Gravity: a force of attraction between objects that is due to their masses

• All Matter experiences gravity because gravity is caused by having mass

  • The amount of gravity is directly related to the amount of mass an object has

What is the Law of Universal Gravitation?

• Sir Isaac Newton was the first to describe gravity and its relationship with objects

  • Watched an apple falling from a tree, and realized that there had to be some force that pulls objects to the Earth

• Newton summarized his ideas as the Law of Universal Gravitation

  • Gravity depends on the masses of the objects and the Distance between them

How Does Mass Affect Gravity?

• The Gravitational force between objects depends on the mass of the two objects

• Mass and gravity have a direct relationship with each other. As one increases, so does the other at the same rate

  • It is easier to lift a smaller object than a larger object

How Does Distance Affect Gravity?

• Gravity and Distance have an indirect relationship

  • As you increase the distance between two objects, the amount of gravity between them decreases by the distance squared (d²)

• The indirect relationship is why objects fall back down to Earth, even though there are larger planets and stars in the solar system

What is the Difference Between Mass & Weight?

• Mass: The measure of the amount of Matter in an object

  • Can not be changed without directly changing the object itself

• Weight: A measure of the gravitational force on an object

  • weight can be easily changed by changing the location of the object

How Does Gravity Affect Falling Objects?

• Gravity can cause an object to move because it is a type of force

• Gravity acts on objects even if they are not moving due to other forces

• In Ancient times, it was thought that the larger an object is, the faster it falls

  • Galileo performed experiments that disproved this idea, showing that all objects will hit the ground at the same time if dropped from the same height

Multiple Choice

How much gravity an object has depends on its _________.

• Weight

• Speed

• Momentum

• Mass

Multiple Choice

Which of the following has the strongest gravitational pull?

• A bowling ball

• A car

• The Earth

• The Sun

Multiple Choice

What scientist is credited with first describing the mathematics of gravity?

• Thomas Edison

• Robert Hooke

• Galileo

• Isaac Newton

Multiple Choice

What do we call the force of gravity on an object?

• Weight

• Mass

• Speed

• Acceleration

Multiple Choice

When will gravity be the strongest?

• The further away you are from an object

• The closer you are to an object

• The faster your relative speed is to an object

• None of the above

How Much Acceleration Does Gravity Cause?

• All objects accelerate toward Earth at the rate of 9.8 m/s²

  • Every second, an object falls, its velocity increases by 9.8 m/s

What is the Velocity of a Falling Object?

• If an object starts at rest, you can relate the velocity, time, and acceleration of the object from Gravity to determine different facts about the movement of the object

  • V_f = Final Velocity

  • g = acceleration due to gravity = 9.8 m/s²

  • t =Time

Calculating Motion with Gravity Sample Problem 1

• A rock is dropped from the top of a cliff. It takes 4 seconds to hit the ground. What was the velocity of the rock on impact?

  • Step 1: Identify the equation we want to use

    • V_f = g × t

  • Step 2: Identify the Variables that we know

    • V_f =?

    • g = 9.8

    • t = 4 seconds

  • Step 3: Plug your values into your equation and solve

Fill in the Blanks

A rock is dropped from the top of a cliff. It takes 4 seconds to hit the ground. What was the velocity of the rock on impact?

Calculating Motion with Gravity Sample Problem 2

• A construction worker is building a bridge and drops a bolt from the top of the bridge. When the bolt hits the ground, it was moving 49 m/s. How long did it take the bolt to fall?

  • Step 1: Identify the equation we want to use

    • V_f = g × t

      • Can we rearrange this to make it easer?

Multiple Choice

How can we rearrange the following equation to solve for time: V_f = g × t

• t =V_f + g

• t = g / V_f

• t = V_f - g

• t = V_f / g

Calculating Motion with Gravity Sample Problem 2

• A construction worker is building a bridge and drops a bolt from the top of the bridge. When the bolt hits the ground, it was moving 49 m/s. How long did it take the bolt to fall?

  • Step 1: Identify the equation we want to use

    • t = V_f / g

  • Step 2: Identify the Variables that we know

    • V_f = 49 m/s

    • g = 9.8

    • t = ?

  • Step 3: Plug your values into your equation and solve

Fill in the Blanks

A construction worker is building a bridge and drops a bolt from the top of the bridge. When the bolt hits the ground, it was moving 49 m/s. How long did it take the bolt to fall?

Calculating Motion with Gravity Sample Problem 3

• A rock at rest falls off a cliff and hits the ground after 3.5 s. What is the

  rock’s velocity just before it hits the ground?

  • Step 1: Identify the equation we want to use

    • V_f = g × t

  • Step 2: Identify the Variables that we know

    • V_f =

    • g =

    • t =

Calculating Motion with Gravity Sample Problem 3

• A rock at rest falls off a cliff and hits the ground after 3.5 s. What is the

  rock’s velocity just before it hits the ground?

  • Step 1: Identify the equation we want to use

    • V_f = g × t

  • Step 2: Identify the Variables that we know

    • V_f = ?

    • g = 9.8

    • t =3.5

Fill in the Blanks

A rock at rest falls off a cliff and hits the ground after 3.5 s. What is the rock’s velocity just before it hits the ground?

How Does Air Resistance Affect Falling Objects?

• Gravity causes objects of different masses to fall at the same rate, but other factors can alter the motion of an object

  • Think of dropping a ball and a piece of paper

• Air Resistance: A force that opposes the motion of falling objects

  • Caused by air making contact with the surface of an object and pushing opposite the motion

  • Affected by:

    • Size/Shape of Object

    • Speed of Object

What is Terminal Velocity?

• As the speed of a falling object increases, air resistance also increases

• At some point, air resistance will increase to the point where it is equal to the force of gravity on the object

  • The object will continue to move, but will no longer accelerate

• Terminal Velocity:  is the speed of an object when the force of air resistance equals the force of gravity

  • The object maintains a constant speed as it falls and has a net force of 0

What is Free Fall?

• Free Fall: The motion of an object when gravity is the only force acting on the object

• Only occurs in when air resistance in negligible, like outerspace

Orbiting Objects are in Free Fall

• Recall: Weight measures how much gravity pulls on an object

  • All objects exert gravity on all other objects, because they all have mass

• As an object moves farther away from Earth, Earth still pulls on the object along with every other object in space

• If an object starts movement with enough force, it will fall at the same rate that the Earth Curves and orbits the object

• Orbit: a curved path around an object

What Motions Combine to make an Object Orbit?

• When an object is in orbit, it goes around another object in space

  • The only way for this to happen is for the orbiting object to have forces balanced so that it will continue to move at the same velocity forever

• Centripetal Force: The force that keeps an object moving in a circular path

What is Projectile Motion?

• Projectile Motion: The curved path that an object follows when thrown, launched, or otherwise projected near the surface of Earth

• All Projectile Motion has two parts to it

  • A Horizontal motion

  • A Vertical Motion from gravity

• Can be drawn out on a Free Body diagram

Multiple Choice

A(n) _____ is the curved path of an object around a point/object in space.

• orbit

• rotation

• revolution

• phase

Multiple Choice

A person would weigh less on the moon than on the Earth because...

• the moon has less mass, and therefore less gravity
• the moon has more mass, and therefore less gravity
• the moon has less mass, and therefore more gravity
• the moon has more mass, and therefore more gravity