# What is Inertia?  Sir Isaac Newton discovered gravity and that all objects have inertia  Inertia is the tendency of an object to stay at rest or in motion.

## Presentation on theme: "What is Inertia?  Sir Isaac Newton discovered gravity and that all objects have inertia  Inertia is the tendency of an object to stay at rest or in motion."— Presentation transcript:

What is Inertia?  Sir Isaac Newton discovered gravity and that all objects have inertia  Inertia is the tendency of an object to stay at rest or in motion  Place a book on your desk. Does it move?  Unless you move the book, it will remain where you put it without moving  Imagine a spacecraft moving through space  When the engines are turned off, the spacecraft will coast through space at the same speed in the same direction  Both the book and the spacecraft have inertia  Because of inertia, an object at rest tends to stay at rest  An object in motion tends to keep moving at a constant speed in a straight line

The Effects of Inertia  You can feel the effects of inertia everyday  Suppose you are riding in a car  What happens when the car comes to a sudden stop?  Your body has inertia.  When the car stops, you keep moving forward- this is why we wear seatbelts!  What happens when the car starts moving again?  Your body tends to stay at rest when the car moves forward, and you feel like you are pushed back into your seat  In baseball, inertia tends to keep a player running in a straight line  This is why runners have to “round” the bases instead of making sharp turns

Inertia and Mass  The more massive an object, the more inertia it has  Example: a bus would need more force to slow it down than a bicycle because the bus is more massive. The bus would also need more force to set it into motion. Therefore, the bus has more inertia.  Bowling balls are made to be heavy so that once they are in motion, they will be difficult to stop  Also, the greater an object’s mass and speed, the greater its momentum.  Momentum is a measure of difficult it is to stop an object.  Often, objects with greater inertia have greater momentum.

Newton’s 1 st Law of Motion  Newton’s 1 st law of motion explains how inertia affects moving and nonmoving objects  Newton's 1 st law states that an object will remain at rest or move at a constant speed in a straight line unless it is acted on by an unbalanced force  An unbalanced force is needed to move the book on your desk  You could supply the force by pushing the book  An unbalanced force is needed to change the speed or direction of the spacecraft  This force could be supplied by the spacecraft’s engines  An unbalanced force could set an object into motion or put it at rest

Balanced and Unbalanced Forces  Balanced forces are forces that are equal in size but opposite in direction  If forces are equal and opposite, an object will remain at rest or in motion  Unbalanced forces are forces that are not equal in size and/or direction and cause a change in motion of an object  When unbalanced forces act on an object at rest, the object will move  When unbalanced forces act on a moving object, the speed or direction will change

Balanced Forces / Unbalanced Forces A.A. B.B.

 The forces of Thrust, Drag, Lift, and Weight are necessary for flight  To give an airplane lift, air pressure below the wings must be greater than the air pressure above the wing.  This makes the forces unbalanced, and sets the plane moving upward  To keep the airplane in motion, forces of Lift, Weight, Thrust, and Drag must stay balanced How does Newton’s 1 st Law demonstrate Flight?

Explain how the picture below demonstrates Newton’s 1 st Law of Motion _______________________________________________________________

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