Newton's First Law of Motion: Inertia

1. Newton’s First Law of Motion—Inertia Newton’s First Law of Motion—Inertia Chapter 4 Chapter 4

2. Aristotle (4 th Century B.C.) Aristotle (4 th Century B.C.)  Believed in two different types of motion: natural motion & violent motion  Believed in two different types of motion: natural motion & violent motion  Natural Motion – either straight up or straight down, objects would seek out their natural resting places (it was “natural” for heavy things to fall and light things to rise)  Natural Motion – either straight up or straight down, objects would seek out their natural resting places (it was “natural” for heavy things to fall and light things to rise)  Violent Motion – imposed motion, result of forces that pushed or pulled  Violent Motion – imposed motion, result of forces that pushed or pulled  The proper state of objects was that of rest.  The proper state of objects was that of rest.

3. Aristotle Aristotle

4. Copernicus (1473-1543 A.D.) Copernicus (1473-1543 A.D.)  Because Earth was already in its natural resting place, it could not move (there was no force big enough to move Earth)  Because Earth was already in its natural resting place, it could not move (there was no force big enough to move Earth)  Copernicus concluded that the only way to make sense of the way the planets move is to assume that Earth and the other planets move around the sun  Copernicus concluded that the only way to make sense of the way the planets move is to assume that Earth and the other planets move around the sun  He worked in secret to avoid being persecuted by the church  He worked in secret to avoid being persecuted by the church

5. Copernicus Copernicus

6. Galileo Galileo  The foremost scientist of the late- Renaissance in Italy  The foremost scientist of the late- Renaissance in Italy  Outspoken in his support of Copernicus, later put on trial and confined to house arrest  Outspoken in his support of Copernicus, later put on trial and confined to house arrest  A force is any push or pull  A force is any push or pull  Friction – the force that acts between materials that touch as they move past each other  Friction – the force that acts between materials that touch as they move past each other  If friction were absent, an object would need no force to remain in motion  If friction were absent, an object would need no force to remain in motion

7. Galileo Galileo

8. Galileo’s Inclined Planes Galileo’s Inclined Planes  Noted that a ball that rolls down an inclined plane picks up speed  Noted that a ball that rolls down an inclined plane picks up speed  When the same ball rolls up the inclined plane, it slows down  When the same ball rolls up the inclined plane, it slows down  When a ball rolls on a flat horizontal surface, it rolls at near constant velocity  When a ball rolls on a flat horizontal surface, it rolls at near constant velocity  Stated that with the absence of friction, the ball would roll forever  Stated that with the absence of friction, the ball would roll forever

9. Galileo’s Inclined Planes Cont. Galileo’s Inclined Planes Cont.  If you have two inclined planes face each other, a ball rolled down one plane will reach nearly the same height as it rolls up the other plane  If you have two inclined planes face each other, a ball rolled down one plane will reach nearly the same height as it rolls up the other plane  He noticed that the ball ended up at the same height, even is the plane was elongated or at a different angle  He noticed that the ball ended up at the same height, even is the plane was elongated or at a different angle  Inertia – the property of a body to resist change (the tendency of a moving body to keep moving and every material object resists change to its state of motion)  Inertia – the property of a body to resist change (the tendency of a moving body to keep moving and every material object resists change to its state of motion)

10. Inclined Planes Inclined Planes

11. Newton’s First Law Newton’s First Law  Every object continues in a state of rest, or of motion in a straight line at constant speed, unless it is compelled to change that state by forces exerted upon it.  Every object continues in a state of rest, or of motion in a straight line at constant speed, unless it is compelled to change that state by forces exerted upon it.  An object will keep doing what it’s already doing  An object will keep doing what it’s already doing  Toss an object out the door of the International Space Station, and it will keep moving at the speed you threw it at forever (no friction in space)  Toss an object out the door of the International Space Station, and it will keep moving at the speed you threw it at forever (no friction in space)

12. Newton’s 1 st Law Newton’s 1 st Law

13. The Law of Inertia The Law of Inertia

14. The Law of Inertia The Law of Inertia

15. Pioneer and Voyager Pioneer and Voyager  After they initially were sent into space, these two spacecraft utilize Newton’s Law of Inertia to move through space  After they initially were sent into space, these two spacecraft utilize Newton’s Law of Inertia to move through space  They are now cruising outside of our solar system  They are now cruising outside of our solar system

16. Mass – A Measure of Inertia Mass – A Measure of Inertia  The amount of inertia an object has depends on its mass—which is roughly the amount of material present in the object  The amount of inertia an object has depends on its mass—which is roughly the amount of material present in the object  Mass is NOT volume, the measure of space that an object takes up  Mass is NOT volume, the measure of space that an object takes up  Mass is NOT weight, the force of gravity on an object  Mass is NOT weight, the force of gravity on an object  Mass is a measure of the inertia that an object exhibits in response to any effort made to start it, stop it, or otherwise change its state of motion  Mass is a measure of the inertia that an object exhibits in response to any effort made to start it, stop it, or otherwise change its state of motion  Mass and weight may not be the same, but they are proportional to each other  Mass and weight may not be the same, but they are proportional to each other Weight = mass x acceleration due to gravity Weight = mass x acceleration due to gravity Measured in Newtons (N) Measured in Newtons (N) A 1-kg bag of nails weighs 9.8 N on the surface of Earth (2.2 lbs.) A 1-kg bag of nails weighs 9.8 N on the surface of Earth (2.2 lbs.)

17. Net Force Net Force  In the absence of a net force , objects do not change their state of motion  In the absence of a net force , objects do not change their state of motion  If you push with equal and opposite forces on opposite sides of an object at rest, it will remain at rest  If you push with equal and opposite forces on opposite sides of an object at rest, it will remain at rest  Net Force – the combination of all forces acting on an object  Net Force – the combination of all forces acting on an object  We use force diagrams to figure out the net force  We use force diagrams to figure out the net force

18. Force Diagrams Force Diagrams

19. Equilibrium Equilibrium  If only the force of gravity was acting on an object at rest, the object would constantly be in free fall  If only the force of gravity was acting on an object at rest, the object would constantly be in free fall  The fact that the object is at rest means that another force must be acting upon it  The fact that the object is at rest means that another force must be acting upon it  The other force exactly balances out the weight of the object and produces a net force of zero  The other force exactly balances out the weight of the object and produces a net force of zero  The other force is called the support force , or normal force  The other force is called the support force , or normal force  Equilibrium – the net force on an object is zero  Equilibrium – the net force on an object is zero

20. Equilibrium Equilibrium

21. Vector Addition of Forces Vector Addition of Forces  We can use the same vector addition techniques on forces as we did on velocities!  We can use the same vector addition techniques on forces as we did on velocities!  Force, like velocity has a magnitude and a direction  Force, like velocity has a magnitude and a direction  For any pair of scales, ropes, or wires supporting a load, the greater the angle from the vertical, the larger the tension force in them  For any pair of scales, ropes, or wires supporting a load, the greater the angle from the vertical, the larger the tension force in them  The resultant of the tension forces in a rope must be equal and opposite to the load being supported  The resultant of the tension forces in a rope must be equal and opposite to the load being supported

22. Vector Addition of Forces Vector Addition of Forces

23. Assignment (Due Wednesday 10/7) Assignment (Due Wednesday 10/7)  Read Chapter 4 (pg. 43-55)  Read Chapter 4 (pg. 43-55)  Do Ch. Assessment #21-39 (pg. 57-58)  Do Ch. Assessment #21-39 (pg. 57-58)  Appendix F #1-10 (pg. 665-666)  Appendix F #1-10 (pg. 665-666)