Gravity and Momentum Turk

What is Weight? Weight is the pull of gravity on an object

Mass versus Weight Mass is the amount of matter in an object Mass is constant Mass is measured in grams or kilograms Weight is the pull of gravity on an object Weight is NOT constant and will change if gravity changes When might the pull of gravity change?

When might the pull of gravity change? On earth, weight becomes less as the distance from the center of the earth increases.

Law of Gravity Credited to Sir Issac Newton According to Newton’s Law of Gravity: Every object in the universe pulls on every other object

Mass versus Weight

Gravity depends upon two factors: Mass 2. Distance The greater the mass the greater the pull of gravity The greater the distance between the objects the less the pull of gravity

Which exerts the strongest pull of gravity on us in the solar system?

A. It would be Zero on Jupiter Jupiter has more mass than Earth. Which of these statements would be true about the force of gravity on you, if you were able to visit Jupiter? A. It would be Zero on Jupiter B. It would be smaller, but not zero, on Jupiter C. It would be the same on Jupiter D. It would be larger on Jupiter

Gravity: Gravity is a force that acts between any two masses Gravity can act over long distances, unlike friction. Earth’s gravity acts downward toward the center of Earth. An upward force usually balances the downward force.

Weight Practice Problem: The strength of gravity at the Earth's surface is almost 10 newtons per kilogram. Calculate the weight of a car with a mass of 2000kg. Solution: = 2000 kg × 10 m/s2 = 20 000 kg*m/s2 or Newtons A measure of the pull of gravity on an object Represented by this formula Fg = m * g Where g is a constant. The acceleration due to gravity 9.8 m/s/s

Consider this: F = m a Compare the weight formula to Newton’s 2nd Law The weight formula is basically the same! Weight (Fg) has been substituted for Force (F), and acceleration due to gravity (g) has been substituted for acceleration (a). Compare the weight formula to Newton’s 2nd Law   Fg = m * g F = m a

Free-falling objects: Free fall is the movement of an object toward the Earth because of gravity. Acceleration of an object due to gravity is 9.8 m/s2 This is independent of an object’s mass! All objects fall toward earth at 9.8 m/s2

Free-falling objects: Gravity causes objects to accelerate downward, whereas air resistance acts in the direction opposite to the motion and reduces acceleration.

Terminal Velocity Terminal velocity is the constant velocity of a falling object when the force of air resistance equals the force of gravity.

Which falls faster? http://the elephant and the feather

Projectile Motion Projectile Motion is the curved path of an object in free fall after it is given an initial forward velocity.

What forces act on any projectile? Once in motion, only 2 forces are acting on a projectile: Air resistance gravity

Describe the path of a projectile. The combination of an initial forward velocity and the downward vertical force of gravity causes the ball to follow a curved path.

Path of a projectile: Earth’s gravitational force makes the ball move down towards the centre of the Earth.

Famous Question: If you drop a bullet and fire a bullet horizontally at the exact same time, which one hits the ground first? http://dsc.discovery.com/videos/mythbusters- dropped-vs-fired-bullet.html OR https://www.youtube.com/watch?v=D9wQVIEdKh8

Momentum Momentum is the product of an object’s mass and its velocity refers to the quantity of motion that an object has. If an object is in motion (on the move) then it has momentum. Momentum can be defined as "mass in motion”. All objects have mass; so if an object is moving, then it has momentum - it has its mass in motion. Which has more momentum traveling at 55 mph?

Momentum Momentum is a vector quantity WHY? mass • velocity In physics, the symbol for the quantity momentum is the lower case "p". Thus, the above equation can be rewritten as: p = m • v Momentum is a vector quantity WHY? The amount of momentum which an object has is dependent upon two variables: mass and velocity. In terms of an equation, the momentum of an object is equal to the mass of the object times the velocity of the object.

Because it has magnitude and direction

Law of Conservation of Momentum If no net force acts on a system, then the total momentum of the system does not change. In a closed system, the loss of momentum of one object equals the gain in momentum for another object – momentum is conserved.

Momentum Practice Problems: Determine the momentum: a. 60-kg halfback moving eastward at 9 m/s. b. 1000-kg car moving northward at 20 m/s. c. 40-kg freshman moving southward at 2 m/s. A. p = m*v = 60 kg*9 m/s p = 540 kg•m/s, east  B. p = m*v = 1000 kg*20 m/s p = 20 000 kg•m/s, north   C. p = m*v = 40 kg*2 m/s p = 80 kg•m/s, south