Gravity and The Law of Universal Gravitation 3.1.2

What is Gravity? Gravity is an attractive force between any two objects that depends on the masses of the objects and the distance between them. Gravity increases: as the mass increases as the distance decreases

Who experiences more gravity - the astronaut or the politician? Which exerts more gravity - the Earth or the moon? more mass less distance

The Law of Universal Gravitation The law of universal gravitation lets us find the force of gravity between any two objects if their masses and the distance between them are known.

F = G m1 m2 d2 F = gravitational force G = universal gravitational constant variable d = distance between the two masses,m1 and m2 Enables the force of gravity to be calculated between 2 objects

The Gravitational Field Gravity is called a long-range force. Gravity never disappears. All objects are surrounded by a gravitational field. The strength of the gravitational field (g) is 9.8 N/kg near Earth’s surface and gets smaller as you move away from Earth. g = 9.8 N/kg N – Newton 1 N = 1 kg . m/s2

Is there a difference between weight and mass? the force of gravity on an object Mass measure of the amount of matter in an object Weight and mass are related. The greater an object’s mass, the stronger the gravitational force between the object and Earth.

Would you weigh more on Earth or Jupiter? Jupiter because... greater mass greater gravity greater weight

Fg = mg Weight the force of gravity on an object WEIGHT MASS Fg - weight (N) m - mass (kg) g - acceleration due to gravity (m/s2) WEIGHT depends on gravity (N) MASS always the same (kg)

m = 5000 kg g = 9.8 N/kg Fg = elephants weight Fg = mg An elephant has a mass of 5000 kg. What is the elephant’s weight? What is given? What is unknown? Which formula? Set up problem and show work. Does your final answer have the correct unit? m = 5000 kg g = 9.8 N/kg Fg = elephants weight Fg = mg Fg = 5000 kg . 9.8 N/kg Fg = 49,000 N

What is the gravitational force exerted on an object called? Assessment What is the gravitational force exerted on an object called? 1. centripetal force A friction B momentum C weight D CORRECT

The spacecraft is in free fall. Assessment 2. Which explains why astronauts seem weightless in orbit? Earth’s gravity is much less in orbit. A The spacecraft is in free fall. B CORRECT The gravity of Earth and the Sun cancel. C The centripetal force on the shuttle balances Earth’s gravity. D

Assessment 3. Which term best describes the forces on an object with a net force of zero? balanced forces A CORRECT unbalanced forces B inertia C acceleration D

Which body exerts the strongest gravitational force on you? Assessment 4. Which body exerts the strongest gravitational force on you? the Moon A Earth B CORRECT the Sun C this book D

Assessment 5. The graph shows the speed of a car moving in a straight line. Over which segments are the forces on the car balanced? A and C A B and D B CORRECT C and E C A, C, and E D

Which of the following is not a force? Assessment 6. Which of the following is not a force? weight A friction B momentum C CORRECT air resistance D