Mass, Weight, and Gravity IP 670

Turn to a partner and discuss What is mass?

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.

Turn to a new partner and discuss… What is inertia?

Inertia is… 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.

Turn to another partner and discuss: What is “the force of gravity”?

The Force of Gravity is … the force of attraction which any two objects that have mass exert on each other. only noticeable when at least one of the objects has a very, very large mass.  When dealing with situations on Earth, we are only interested in the gravitational force that Earth exerts on objects.

Newton’s Law of Universal Gravitation

Three Things for you to know:  bigger if the objects have more mass.  smaller if the objects are farther apart.  universal. It applies to ANY two objects which have mass.

Why is gravity so special? It is universal. It does not require contact. It is poorly understood. Note: When people say “gravity” they typically mean “the force of gravity.” Remember that we are talking about a force.

One more partner question… What is weight?

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.

Weight Calculations To calculate weight, use the following formula: Weight = force of gravity (in Newtons) m = mass (in kilograms) g = acceleration due to gravity  depends on the planet and the exact location.  On Earth, g = 10 m/s 2

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.

True and False 1. More massive objects have more inertia than less massive objects. 2. If the forces acting upon an object are balanced, then it must be at rest. 3. On Earth, the force of gravity acting upon an object is 10 times the weight of the object. T F F

More True and False… 4. Inertia is a force which acts upon objects at rest. 5. A feather and an elephant will have the same weight within a vacuum. 6. If you stand on a bathroom scale and bounce, the scale reading changes. This means that you weigh differently ( more or less) than if you were to standing at rest. F F F

More True and False… 7. More massive objects have the same inertia as less massive objects; yet more massive objects will weigh more. 8. The weight of an object can be expressed in units of kilograms or grams. 9. Weight and mass are the same thing; it's just that they have different values on different planets. F F F

More True and False… 10. You and your lab partner will experience a force of gravitational attraction when standing next to each other. T