8.2.3-Newton's 2nd Law of Motion

Objectives:

^1. I understand the difference between acceleration and velocity.

^2. I can describe the relationship between acceleration and force.

^3. I can describe the relationship between acceleration and mass.

Multiple Choice

What is the SI Unit of Force?

• Gram

• Meter

• Newton

• m/s

© Kesler Science, LLC

Newton’s Second Law or

Law of Force and Acceleration

The acceleration (a) of an object is

dependent upon two variables:

a. the net force (F)
b. the mass of the object (m)

F

m x a

Newton’s Laws of Motion

© Kesler Science, LLC

Newton’s Laws of Motion

Newton’s Second Law (cont.)

•

Acceleration is produced when a
force acts on a mass

•

The greater the mass of the object
being accelerated the greater the
amount of force needed to
accelerate the object

m

F

x a

What does the “a” represent?

Fill in the Blanks

A 10 kg bowling ball would require what force to accelerate down an alleyway at a rate of 3 m/s² ?

Fill in the Blanks

What is the mass of a falling rock if it produces a force of 147 N? (Hint: all objects accelerate at 9.8 m/s² due to gravity)

Fill in the Blanks

What is the acceleration of a softball if it has a mass of 0.5 kg and hits the catcher's glove with a force of 25 N?

Fill in the Blanks

Your own car has a mass of 2000 kg. If your car produces a force of 5000 N, how fast will it accelerate?

Fill in the Blanks

Sally challenges you to a race. On the first turn you run off the course and your car strikes a large bale of hay. Your car still produces 5000 N of force, but now it accelerates at only 2 m/s² . What is the mass of your car now that the bale of hay is stuck to it?

Multiple Choice

What was the mass of the bale of hay?

• 300 kg

• 500 kg

• 500 g

• 500 N

Multiple Choice

The mass of a helicopter is 4,500 kg and the net force on it is 18,000 N. At what rate is the helicopter accelerating?

$$f\ =\ m\times a$$  

• $$4,500\ =\ 18,000\ \times\ a$$

  $$4,500\div18,000\ =\ 0.25\ m/s^2$$  

• $$18,000\ =\ 4,500\ \times\ a$$

  $$18,000\div4,500=4\ m/s^2$$  

Multiple Choice

A car is being towed. What is the car's mass if the net force on the car is 4,000 N and it has an acceleration of 2.5 m/s²?

$$f=m\times a$$  

• $$4000\ N\ =\ m\times2.5$$  

  $$4000\div2.5\ =\ 1,600\ kg$$

• $$4,000\ N\ =\ m\times2.5$$  

  $$4,000\ \times2.5\ =\ 10,000\ kg$$

Multiple Choice

What is the net force on a car with a mass of 1000kg, if it accelerates at 35 m/s²?

$$f\ =\ m\times a$$  

• 1000x35 = 35,000 N

• 1000/35 =

  28.6 N

Newton’s 2nd Law of Motion

• 2nd Law States that a

force on an object will move the object in the direction of the force.

• F = m x a

UNIT for Force:
Newtons (N)
UNIT for mass:
Kilograms (Kg)
UNIT for acceleration:
m/s²

Force

• A force is a push or

a pull.

• F = m x a

(A) 4 N
(B) 8 N
(C) 20 N
(D) 40 N

A man hits a golf ball (0.2 kg)
which accelerates at a rate of
20m/s/s. What amount of force
acted on the ball?

Multiple Choice

What is the formula for the 2nd law of motion?

• a = lw

• F = mama

• F = ma

• F = llama

Multiple Choice

A 20 kg bike accelerates at 10 m/s². what was the force?

F = m x a

• 25 Newtons

• 20 Newtons

• 200 Newtons

• 10 Newtons

Multiple Choice

7.) An object with a mass of 120 kg. has a force of 12,000 newtons applied to it. What is the resulting acceleration of the object?

• 150 m/s²

• 200 m/s²

• 100 m/s²

Multiple Choice

The masses of four objects are given in this table. If all objects are struck with the same amount of force, which one will have the greatest acceleration?

• Object 1
• Object 2
• Object 3
• Object 4

​Review - Newton's 1st Law - Law of Inertia

​

​An object at rest stays at rest,

​

​An object in motion stays in motion,

​

​Unless acted on by an unbalanced force.

Multiple Choice

What is Newton's First Law known as? The Law of

• Friction
• Mass
• Inertia
• Gravity

Multiple Choice

What is Newton's First Law

• F=ma

• Every action has an equal and opposite reaction

• An object at rest stays at rest, an object in motion stays in motion, unless acted on by an unbalanced force

• Friction

Multiple Choice

A person is pushed forward into their seatbelt when a car suddenly stops

• 1st Law

• 2nd Law

• 3rd Law

Multiple Choice

A steel ball is at one end of a box that is moving forward as shown. The box suddenly stops. According to Newton's first law, what happens to the steel ball just after the box stops?

• Because of friction, the ball continues rolling forward at the same speed.

• Because of friction, the ball rolls forward at an increase speed.

• Because of inertia, the ball continues rolling forward at the same speed.

• Because of inertia, the ball rolls forward at an increased speed.

Multiple Choice

The ______ the mass of an object, the ______ force it will take to accelerate.

• smaller, more

• greater, more

• greater, less

• smaller, less

Multiple Choice

The larger the mass you have the _____ force you need to change its motion.

• more
• less

Multiple Choice

According to Newton's second law, if you increase the force applied to an object :

• it accelerates more
• it doesn't move
• you get more inertia
• it decelerates

Multiple Choice

If both rocks are pushed with the same amount of force, which rock would accelerate more?

• The 400kg Rock because it weighs more.

• The 40kg rock because it weighs less.

Multiple Choice

Which grocery basket will have the least acceleration, if both grocery baskets are pushed with the same amount of force?

• The one without groceries because it has more mass.

• The one with groceries because it has more mass.

• The one without groceries because it has the least mass.

• The one with groceries because it has least mass.

Multiple Choice

If the man pushes with an equal amount of force, which object will accelerate more?

• Car because it has more mass

• Lawnmower because it has less mass

• Car because it has less mass

• Lawnmower because it has more mass

Multiple Choice

A force of 90N is applied to each cart below, which one will accelerate the fastest?

• Cart 1
• Cart 2
• Cart 3 
• Cart 4

Multiple Choice

Why would one ball travel a greater distance than the other when pushed with the same amount of force?

• Different sizes
• Different weights
• Different masses
• Different forces

Multiple Choice

Will it take more force to push an empty shopping cart or a shopping cart that is full?

• The empty shopping cart
• The full shopping cart
• They will take the same amount of force

Newton's first law says that an object at rest stays at rest unless a force is added to change its motion. But what kind of change happens?

​

​

The answer is acceleration.

Acceleration - rate at which velocity changes with time, in terms of both speed and direction.

Acceleration is different from velocity.

Velocity is the speed of something in a direction at a particular time.

​

Acceleration is the CHANGE in velocity over a certain distance

Acceleration isn't just when somethings speeds up!

It's also when it slows down and changes direction.

Any change in velocity is a change in acceleration.

Newton's 2nd Law of Motion

f=m*a

Force = mass * acceleration​​

​

acceleration of an object is directly proportional to the net force and inversely proportional to its mass. 

Newton's 2nd Law

F=m*a

Newton's 2nd Law of Motion has 3 parts

¹Acceleration is the result of unbalanced forces.

²A larger force makes a proportionally larger acceleration.

³Acceleration is inversely proportional to mass.

³Acceleration is inversely proportional to mass.

*INVERSELY kind of means opposite. This means that acceleration is oppositely related to mass. When one goes up, the other goes down. This is their relationship.

³Acceleration is inversely proportional to mass.

For example, this guy easily lifts this little car and knocks it over. But, if we increase the mass and made it a large truck and he used the same force, it wouldn't accelerate as much. This is because acceleration and mass are inversely related.

Draw

Circle the graph that represents the relationship between force and acceleration.

Draw

Circle the graph that represents the relationship between mass and acceleration.

³Acceleration is inversely proportional to mass.

REMEMBER: as mass increases, so does the object's inertia.

SINCE inertia is an objects resistance to change in velocity...

THEN an increase mass would also resist acceleration.

KEY POINTS!

^1. The net force is what causes acceleration.

^2. If there is no acceleration, the net force must be zero.

^3. If there is acceleration, there must also be a net force.

^4. Force causes acceleration.

^5. Mass resists acceleration.

Multiple Choice

A skydiver is moving downward with decreasing speed as her parachute opens.

Which statement describes the skydiver's motion?

• The skydiver is accelerating.

• The skydiver has a constant velocity.

Acceleration isn't just when somethings speeds up!

Multiple Choice

Which of the following boxes are accelerating? Select all that apply.

• A box of books that a woman is pushing across the floor with increasing speed.

• A box of jewelry that a girl is holding still in her lap.

• A box of cereal that is moving along a straight conveyor belt at a steady speed.

It's also when it slows down and changes direction.

Any change in velocity is a change in acceleration.

Draw

Draw an example of an object accelerating by speeding up, slowing down, or changing directions.

Remember, velocity is a vector

This means it contains speed and direction. So changing direction, even when staying at the same speed, is considered accelerating.

Newton's 2nd Law of Motion

acceleration of an object is directly proportional to the net force and inversely proportional to its mass. 

Newton's 2nd Law of Motion

f=m*a

Force = mass * acceleration​​

​

acceleration of an object is directly proportional to the net force and inversely proportional to its mass. 

Newton's 2nd Law of Motion has 3 parts

¹Acceleration is the result of unbalanced forces.

²A larger force makes a proportionally larger acceleration.

³Acceleration is inversely proportional to mass.

¹Acceleration is the result of unbalanced forces.

Unbalanced forces are required for motion and acceleration to occur. A net force is when the forces add up to more than zero.

²A larger force makes a proportionally larger acceleration.

​The relationship between force and acceleration.

²A larger force makes a proportionally larger acceleration.

A larger force on something with the same mass, leads to a larger acceleration.

²A larger force makes a proportionally larger acceleration.

This is like saying Fernando Tatis Jr. will accelerate the ball greater than I will, because he will hit the same ball with a much greater force.

²A larger force makes a proportionally larger acceleration.

This is the relationship between force and acceleration. As force increases, acceleration does at the same rate.

³Acceleration is inversely proportional to mass.

*INVERSELY kind of means opposite. This means that acceleration is oppositely related to mass. When one goes up, the other goes down. This is their relationship.

³Acceleration is inversely proportional to mass.

For example, this guy easily lifts this little car and knocks it over. But, if we increase the mass and made it a large truck and he used the same force, it wouldn't accelerate as much. This is because acceleration and mass are inversely related.

Draw

Circle the graph that represents the relationship between force and acceleration.

Draw

Circle the graph that represents the relationship between mass and acceleration.

​Circular Motion

​Circular motion is any motion in which an object is moving along a curved path. There are two primary forces occurring during circular motion: the force of the object moving forward (shown in blue), and the force called centripetal force (shown in red). Each of these forces are constantly causing acceleration in the object.

​Circular Motion

Centripetal force is the force which acts perpendicular to the direction of motion, toward the center of the curve. The motions of satellites and planets are also circular motion and are subject to centripetal force just like a yoyo being spun around or your keys on your lanyard when you spin them.​

Multiple Choice

Centripetal force is indicated by the __________ ray.

• black

• green

Multiple Choice

Which of the following is the correct formula for force?

• f = ma

• f = m/a

• f = a/m

• f = a + m

Multiple Choice

Any object that travels around another object in space is a satellite.

• True

• False

Multiple Choice

Satellites in orbit around the Earth travel in almost circular path because Earth is

• centripetal

• free falling

• curved

• massive

Multiple Choice

An object traveling in a circle is accelerating because it is constantly changing

• speed

• velocity

• direction

• force

Multiple Choice

The force that causes an object to move in a circle is called centripetal force?

• True

• False

Multiple Choice

If you could turn off a centripetal force, ___________ would cause the object to fly off in a straight line.

• inertia

• momentum

• Earth

• force

Multiple Choice

______________ is the centripetal force that causes a satellite to move in a circle.

• String

• Space Shuttle

• Gravity

• Helicopter

Multiple Choice

Any object that travels around another object in space is a satellite.

• True

• False

Multiple Choice

Satellites in orbit around the Earth travel in almost circular path because Earth is

• centripetal

• free falling

• curved

• massive

Multiple Choice

An object traveling in a circle is accelerating because it is constantly changing

• speed

• velocity

• direction

• force

Multiple Choice

The force that causes an object to move in a circle is called centripetal force?

• True

• False

Multiple Choice

If you could turn off a centripetal force, ___________ would cause the object to fly off in a straight line.

• inertia

• momentum

• Earth

• force

Multiple Choice

______________ is the centripetal force that causes a satellite to move in a circle.

• String

• Space Shuttle

• Gravity

• Helicopter