1. WHICH ONE DEPENDS ON THE OTHER? Weight and Mass (or is it Mass and Weight?)

2. True or False 1. The force of gravity is the same for all objects on earth. 2. Gravity is caused by the rotation of the earth. 3. There is no gravity on the moon. 4. In a vacuum there is no gravity. 5. You exert as large a gravitational force on the earth as it exerts on you.

3. Lab What is the mathematical relationship between the gravitational force on an object (aka: its weight) (N) and its mass (kg) on earth?

4. Weight = mass x g The gravitational force on an object (aka: weight of an object) is directly proportional to its mass, as shown by the equation: Fg=9.8m This means if an object’s mass is tripled, its weight triples, and if its mass is halved, its weight is also halved. For example, a 4 kg watermelon would weigh 39.2 N, which is four times the 9.8N that a 1kg mango would weigh.

5. What is weight? The size of the gravitational force on a body, exerted by Earth (or the chunk or matter body is on). NOT 9.8 for all objects NOT the same for all objects The magnitude of the gravitational force Units: N (newton) F g =9.8m or Fg = mg (g = accel. due to gravity) Measured with a spring scale

6. Fg = mg The size (magnitude) of the gravitational force a planet exerts on an object on or near the planet This force acts WITHOUT CONTACT so it cannot be directly measured. SI unit: N (newton) alternate units: pounds, stones, dynes “Measured” with a scale A 1.0kg mass weighs 9.8N Weight is NOT 9.8 for all objects (a 5.okg mass weighs 49N) The force of gravity is NOT the same for all objects! Fg: weight

7. Ex What is the weight (in N) of a 30 kg suitcase? An astronaut weighs 700N on Earth. How much does he weigh on the moon (where g=1.6m/s/s)? A 30 kg child sits on a swing that consists of a level wooden platform suspended by two vertical chains. Determine the tension in each chain if the child positions herself in the exact middle (midway between the chains).

8. But, What IS Mass?

9. But What IS Mass? What is the mathematical relationship between period (s) and mass (kg) for a twin spring inertial balance? Use the balance, and calibration curve to determine the mass of a sample.

10. What is mass? The measure of an object’s resistance to acceleration (inertia) One of the two properties of all matter A SCALAR Measured in kg in the SI system NOT the force of gravity NOT weight Measured by trying to accelerate object

11. Mass is a fundamental property of matter, there is no formula to define it. A measure of the amount of inertia (resistance to acceleration) for an object. Mass is one way to measure how much of something you have. SI unit: kg (kilogram) alternate units: gram, slug 1.0 liter of water has a mass of 1.0kg Mass does NOT change for an object, regardless of where it is in the universe, unless the amount of matter changes m: mass (scalar)