Phys. Sci 5-5 Newtons laws

​Physical Science 5-5: Newton's Laws of Motion

Multiple Choice

What is the unit for Force? 

• N (Newtons)
• lbs (pounds)
• g (grams)
• m/s (meters per second)

Fill in the Blank

What is the average speed of a walker who walks 500 m in 400 seconds?

.

Multiple Choice

Friction can be increased by

• making the surface rough

• making the surface smooth

• adding oil to the surface

• none of these

Multiple Choice

As distance between two objects increase the pull of gravity..... 

• Increases
• Decreases
• Stays the same

Multiple Choice

What type of friction is shown by a car that is at rest?

• rolling

• static

• fluid

• sliding

Multiple Choice

Acceleration occurs when an object changes its speed or ______.

• direction
• force
• inertia
• mass

Fill in the Blank

A car driving at 50 miles per hour drives for 2 hours. How many miles did it travel?

​Lesson Objectives

• Review the concept of Net Force

• Describe what happens to objects with no Net Force

• Show how Mass, force, and acceleration are related

• Describe how force pairs are related using Newton's Third Law

Reviewing Net Force

• Forces are constantly acting on all objects in the universe

  • Unbalanced forces cause a change in an objects motion

• When multiple forces act at the same time, they are added together to calculate how much force is acting on the object

• Net Force: The total force acting on an object

  • If the net force on an object is equal to zero, it can still move, but will not change speed or direction

What is Inertia?

• Inertia: the ability of an object to resist any change in motion

  • A property of matter where objects will continue to do what they are already doing unless there is enough force to overcome the inertia

• Inertia is directly related to the mass of an object

  • Larger objects are harder to move than smaller ones

Newton's First Law of Motion

• Newton's First Law of Motion is called the Law of Inertia.

  • Describes objects with no unbalanced forces acting on them (Net Force = 0)

    • Has two parts to it

      • An object at rest will remain at rest until an unbalanced force acts on it

      • An object moving at a constant velocity will continue to move at a constant velocity until an unbalanced force acts on it

• Newton's first law can be hard to observe on Earth due to the friction acting on moving objects

What is Newton's Second Law of Motion?

• Newton's Second Law of Motion describes how an object moves when an unbalanced force acts on it

• Has two parts

  • The Acceleration of an object depends on the mass of the object

    • Larger masses will have less acceleration than smaller ones

  • The Acceleration of an object depends on the force applied to the object

    • Increasing the amount of force acting on an object increases the acceleration

Writing Newton's Second Law of Motion as an equation

• Newton's second law can be written as an equation with the following variables and units

  • F= Net Force in Newtons

  • m= Mass in kilograms

  • a = Acceleration in m/s²

​Newton's 2nd Law of Motion Sample Problem 1

• What is the acceleration of a 3 kg mass if a force of 14.4 N is used to move the mass?

  • Step 1: Identify which equation we should use

    • We are solving for acceleration, so a=F/m

  • Step 2: Identify which information we know

    • a=?

    • F= 14.4

    • m=3

  • Step 3: Plug values into the equation and solve

Fill in the Blank

What is the acceleration of a 3 kg mass if a force of 14.4 N is used to move the mass?

.

​Newton's 2nd Law of Motion Sample Problem 2

• What Force is needed to accelerate a 1250 kg car at a rate of 40 m/s²?

  • Step 1: Identify which equation we should use

Multiple Choice

Which form of Newton's Second Law is best for the following question: What Force is needed to accelerate a 1250 kg car at a rate of 40 m/s²?

• a=f/m

• m=f/a

• f=m×a

​Newton's 2nd Law of Motion Sample Problem 2

• What Force is needed to accelerate a 1250 kg car at a rate of 40 m/s²

  • Step 1: Identify which equation we should use

    • f=m×a

  • Step 2: Identify which information we know

    • a=

    • F=

    • m=

​Newton's 2nd Law of Motion Sample Problem 2

• What Force is needed to accelerate a 1250 kg car at a rate of 40 m/s²

  • Step 1: Identify which equation we should use

    • f=m×a

  • Step 2: Identify which information we know

    • a= 40 m/s²

    • F= ?

    • m=1250

  • Step 3: Plug into your equation and solv3

Fill in the Blank

What Force is needed to accelerate a 1250 kg car at a rate of 40 m/s² ?

​Newton's 2nd Law of Motion Sample Problem 3

• What is the mass of a truck if it produces a force of 14,000 N while accelerating at a rate of 5 m/s²?

  • Step 1: Identify which equation we should use

Multiple Choice

Which form of Newton's Second Law is best for the following question: What is the mass of a truck if it produces a force of 14,000 N while accelerating at a rate of 5 m/s²?

• a=f/m

• m=f/a

• f=m×a

​Newton's 2nd Law of Motion Sample Problem 3

• What is the mass of a truck if it produces a force of 14,000 N while accelerating at a rate of 5 m/s²?

  • Step 1: Identify which equation we should use

    • m=f/a

  • Step 2: Identify which information we know

    • a=

    • F=

    • m=

  • Step 3: Plug in your values and solve

​Newton's 2nd Law of Motion Sample Problem 3

• What is the mass of a truck if it produces a force of 14,000 N while accelerating at a rate of 5 m/s²?

  • Step 1: Identify which equation we should use

    • m=f/a

  • Step 2: Identify which information we know

    • a= 5 m/s²

    • F= 14,000

    • m=?

  • Step 3: Plug in your values and solve

Fill in the Blank

What is the mass of a truck if it produces a force of 14,000 N while accelerating at a rate of 5 m/s²?

Fill in the Blank

How much force is needed to accelerate a 3kg skateboard at 5m/s²?

Fill in the Blank

An object accelerates 5 m/s² when a force of 20 newtons is applied to it. What is the mass of the object?

Fill in the Blank

If a 10 kilogram object accelerates suddenly at 15 m/s², how much force was applied to the object?

Fill in the Blank

Jenny applies a 60 N force to a 20 Kg cart, what is the acceleration of the cart if friction can be neglected?

Newton's Second Law & Gravity

• Newton's second law explains why objects on Earth all fall with the same acceleration of 9.8 m/s²

• The larger force of gravity will also be divided by the larger mass of the object

What is Newton's Thrid Law of Motion?

• All forces act in pairs

• When one object exerts a force on a second object, the second object exerts the same force back

  • Example: You sit in a chair, and the chair pushes you up with a force equal to your weight

• We call these two forces action and reaction forces

  • Each of the forces acts on a different object

• Newton's Third Law of Motion states: For every action, there is an equal and opposite reaction

How do action and reaction forces work?

• When two objects interact, the action and reaction forces act on different objects

  • How an object is affected depends on the object itself

    • A small object may hit a larger object and have no effect because it needs a larger force to have an effect

Multiple Choice

Which law of motion states that force equals mass x acceleration

• Newtons 1st law

• Newtons 2nd law

• Newtons 3rd law

Multiple Choice

An object moving at a constant velocity will continue moving at a constant velocity unless acted upon by an unbalanced force applies to which law of motion?

• Newtons 1st law

• Newtons 2nd law

• Newtons 3rd law

Multiple Choice

Claims if an object exerts a force on another object, the second object exerts a force of equal strength in the opposite direction back towards the first object

• Newtons 1st law

• Newtons 2nd law

• Newtons 3rd law

Multiple Choice

States an object at rest will remain at rest unless acted on by an unbalanced force

• Newtons 1st law

• Newtons 2nd law

• Newtons 3rd law

Multiple Choice

The swing of a hammer drives a nail partially into a piece of lumber until it comes to a rest. The lumber exerts an opposite force of resistance.

• Newtons 1st law

• Newtons 2nd law

• Newtons 3rd law