What is Inertia?

1. 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

2. 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

3. Inertia and Mass • The more massive an object, the more inertia it has • Example: a bus would needmore 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.

4. Newton’s 1st Law of Motion • Newton’s 1st law of motion explains how inertia affects moving and nonmoving objects • Newton's 1st 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

5. 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

6. Balanced Forces / Unbalanced Forces B. A.

7. How does Newton’s 1st Law demonstrate Flight? • 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

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