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Main » Kinematics & Dynamics » Newton's Laws » Lesson I.6.2

### Newton's Laws of Motion - Lesson I.6.2

 Key Terms: Inertia |Galileo's Thought Experiment |

Inertia
• The property of an object that resists changes in its state of rest or motion.

 When stationary difficult to push. When moving difficult to stop.
 When you are in a car that is accelerating, you feel as if you are being pushed back. Your body (actually the inertia of your body) is resisting the increase in speed. When the car comes to a sudden stop, your body wants to continue in a forward motion.

 Sudden Starts - head rests stop the head from being pushed back. (rapid positive acceleration)

 Sudden Stops - seat belts help your body resist the tendency to keep moving. (rapid negative acceleration)

 When accelerating, the coffee tends to spill on you. When stopping, the coffee tends to spill forward.

• It depends on mass.
 Less Inertia Child on a swing - less inertia More Inertia Adult on a swing - more inertia
• It is easier to push and stop a child on a swing compared to an adult.
• #### Galileo's Thought Experiment

• Galileo developed the concept of inertia.

Inertia is the objects resistance to its change in state of motion or rest.
• By using a pair of inclined planes and a ball (assuming friction was eliminated), Galileo observed that a ball which rolled down one incline would roll up another incline to the same height at which it started.

Galileo's basic thought process was...

 Initial height = Final height Initial height = Final height Initial height should equal final height however …Since that would not be possible here, Galileo, by inductive reasoning, stated that the ball would continue in motion at a constant speed in a straight line forever (trying to achieve the initial height).