Inertia Mass Weight Inertia Inertia What is Inertia

Inertia, Mass, Weight

Inertia

Inertia

What is Inertia? • a property of matter. • a measure of an object’s resistance to changes in its motion. – resistance to changes in speed and/or direction. • directly proportional to an object’s mass. – more massive objects have more inertia.

Mass and Weight How are they different?

Mass is … • the amount of matter in an object. • a measure of the inertia of an object. • measured in units of kilograms. • constant everywhere. §No matter where I take you, your mass doesn’t change.

Weight is … • another name for the force of gravity which the planet exerts on an object near its surface. §We typically speak of our weight on Earth so we are talking about the force of gravity that the Earth exerts on us. • a force. • dependant on BOTH your mass and the planet which you are on or near.

Out in Space How do you “weigh” an astronaut?

“Microgravity” http: //www. youtube. com/watch? v=YFa 8 M 3 fbc 8 c

How to “Weigh” an Astronaut

Weight Calculations • Weight = Mass * (Gravitational Field Strength) • Gravitational Field Strength depends on the planet and the exact location. • On Earth, gravitational field strength = g= 9. 8 N/kg. – In other words, the earth exerts 9. 8 N of force on you for every 1 kg of mass. • On Earth, – Weight (in Newtons) = Mass (in kilograms) * 9. 8 N/kg

English versus Metric Units English Units Mass Kilograms Slugs Weight Newtons Pounds (lbs) Note: 9. 8 Newtons = 2. 2 lbs

Question #1 • Determine the weight (in Newtons) of a 64 kg object on planet Earth.

Question #2 • Determine the mass (in kilograms) of an object which weighs 200 N on planet earth.