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Forces & Newton’s Laws Chapter 11 Notes. Forces / A force is a push or pull exerted on an object / Forces tend to change the motion of an object / A force.

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Presentation on theme: "Forces & Newton’s Laws Chapter 11 Notes. Forces / A force is a push or pull exerted on an object / Forces tend to change the motion of an object / A force."— Presentation transcript:

1 Forces & Newton’s Laws Chapter 11 Notes

2 Forces / A force is a push or pull exerted on an object / Forces tend to change the motion of an object / A force has two components / Magnitude (how much) / Direction (which way) / A force is a push or pull exerted on an object / Forces tend to change the motion of an object / A force has two components / Magnitude (how much) / Direction (which way)

3 Mass vs Weight / Many confuse the difference between mass and weight / Mass = How much matter an object has / Measured typically in grams (or kg) / Weight = Gravitation pull on an object / Weight = mass * gravitational acceleration / Many confuse the difference between mass and weight / Mass = How much matter an object has / Measured typically in grams (or kg) / Weight = Gravitation pull on an object / Weight = mass * gravitational acceleration

4 Mass vs Weight / Take an object of mass 100 kg / On earth the mass = 100 kg / On the moon the mass - 100 kg / In outer space the mass = 100 kg / Weight of same object / On Earth the weight = 980 N / On the moon the weight = 160 N / In outer space the weight = 0 N / Take an object of mass 100 kg / On earth the mass = 100 kg / On the moon the mass - 100 kg / In outer space the mass = 100 kg / Weight of same object / On Earth the weight = 980 N / On the moon the weight = 160 N / In outer space the weight = 0 N

5 Unit of Forces / There are several units that can be used to measure force / Many of you are most familiar with the unit of pound (lb) / The metric unit for force (the one we will use) is the Newton (N) / There are several units that can be used to measure force / Many of you are most familiar with the unit of pound (lb) / The metric unit for force (the one we will use) is the Newton (N)

6 Unit of Force / What is a Newton? / It is a derived unit / It is an abbreviation for: (Kg * m ) / s 2 / What is a Newton? / It is a derived unit / It is an abbreviation for: (Kg * m ) / s 2

7 Net Force / Net forces are more important than individual forces / A net force of the sum total of all the individual forces acting on an object / Net force is written as:∑F / Net forces are more important than individual forces / A net force of the sum total of all the individual forces acting on an object / Net force is written as:∑F

8 Net Force / If the net force is zero the forces are considered to be BALANCED / If the net force is NOT zero the forces are considered to be UNBALANCED / If the net force is zero the forces are considered to be BALANCED / If the net force is NOT zero the forces are considered to be UNBALANCED

9 Balanced vs Unbalanced / When forces are BALANCED the motion of an object will remain constant / When forces are UNBALANCED the motion of an object will change…….it will ACCELERATE / When forces are BALANCED the motion of an object will remain constant / When forces are UNBALANCED the motion of an object will change…….it will ACCELERATE

10 Net Force / Example: / Find the net force if a 300 N force acts to the right and a 120 N force acts to the left / Example: / Find the net force if a 300 N force acts to the right and a 120 N force acts to the left

11 Net Force / Example: / Find the net force if a 400 N force acts to the right, a 120 N force acts to the left, and a 75 N forces acts to the left / Example: / Find the net force if a 400 N force acts to the right, a 120 N force acts to the left, and a 75 N forces acts to the left

12 Friction / Friction is a force that opposes motion / It occurs when two surfaces are in contact / It depends on: / The weight of the object / The type of surfaces / Friction always slows down an object / Friction is a force that opposes motion / It occurs when two surfaces are in contact / It depends on: / The weight of the object / The type of surfaces / Friction always slows down an object

13 Types of Friction / Static friction / Occurs when the surfaces in contact do NOT slide past one another / Kinetic friction / Occurs when the surfaces in contact slide past one another / Static friction / Occurs when the surfaces in contact do NOT slide past one another / Kinetic friction / Occurs when the surfaces in contact slide past one another

14 Kinetic Friction / Kinetic friction is often referred to as sliding friction / If a round object rolls over a flat surface it is often referred to as rolling friction / Kinetic friction is often referred to as sliding friction / If a round object rolls over a flat surface it is often referred to as rolling friction

15 Types of Friction / Static friction is always greater than kinetic/rolling friction / Rolling friction is typically less than sliding friction Static > Sliding > Rolling / Static friction is always greater than kinetic/rolling friction / Rolling friction is typically less than sliding friction Static > Sliding > Rolling

16 Drag / Any object that moves through a fluid (like air) experiences a frictional force called air resistance / Another term for air resistance is DRAG / Any object that moves through a fluid (like air) experiences a frictional force called air resistance / Another term for air resistance is DRAG

17 Friction / Can be harmful / Engine parts / Air resistance / Can be helpful / Warming your hands / Starting/Stopping/Turning / Brillo pads / Can be harmful / Engine parts / Air resistance / Can be helpful / Warming your hands / Starting/Stopping/Turning / Brillo pads

18 Newton’s Laws / Sir Isaac Newton (1643-1727) / Developed Laws of motion / Sir Isaac Newton (1643-1727) / Developed Laws of motion

19 Newton’s Laws / Newton was a student on break when he started to form his thoughts on motion / He challenged the belief system in regard to motion that had been establish over 2000 years ago / Newton was a student on break when he started to form his thoughts on motion / He challenged the belief system in regard to motion that had been establish over 2000 years ago

20 Newton’s Laws / He summarized his thoughts into three Laws of Motion / Law of Inertia / F = ma / Action/Reaction Pairs / He summarized his thoughts into three Laws of Motion / Law of Inertia / F = ma / Action/Reaction Pairs

21 Newton’s 1st Law / An object at rest will stay at rest OR an object in motion will stay in motion UNLESS a NET force acts on the object

22 Newton’s 1st Law / Often referred to as the Law of Inertia / What is Inertia? / property of matter / tendency of an object to resist changes in motion / more mass = more inertia / Often referred to as the Law of Inertia / What is Inertia? / property of matter / tendency of an object to resist changes in motion / more mass = more inertia

23 Newton’s 2nd Law / A net force acting on an object will cause the object to change its motion - it will accelerate / The magnitude of the force and the mass of the object will both influence the acceleration / A net force acting on an object will cause the object to change its motion - it will accelerate / The magnitude of the force and the mass of the object will both influence the acceleration

24 Newton’s 2nd Law / Written as an equation ∑ F = m a / Written as an equation ∑ F = m a

25 Newton’s 3rd Law / For every force there is an EQUAL but OPPOSITE reaction force / Examples / Baseball - Bat / Bug - Windshield / For every force there is an EQUAL but OPPOSITE reaction force / Examples / Baseball - Bat / Bug - Windshield


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