Gravity

• Measured in Newtons (N)

• Pull of gravity on a mass gives an object weight

• To find weight, w=m*g

Universal Law of Gravitational

• Any two objects in the universe are attracted to each other by a force called gravity

• Gravitational force is affect by two factors: (1) mass & (2) distance

• Mass is measured in kilograms and grams

• Distance is measured in kilometers

• Weight is measured in Newtons.

Effect of Mass & Distance on Objects on Gravity

• Mass of an object increases ↑, gravitational force of an object increases ↑

• If distance between objects decreases ↓, gravitational force between objects increase ↑

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Forces that Can Affect Something Falling

• Two forces that affect something falling: gravity & air resistance

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Terminal Velocity

• Force of gravity and force of air resistance are equal to zero

• Acceleration is also zero.

Free Fall

• When the only force acting on a falling body is gravity, it is called free fall.

• Air Resistance → Objects with less surface area will fall faster

• No Air Resistance → in a vacuum (objects will fall at the same rate & gravity only)

Projectile Motion

• Gravity can cause a thrown object to move in a curved, downward path called projectile motion

• Inertia causes ball to move horizontally, gravity causes the ball to move vertically

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Newton's Laws of Motion

Lesson Question: How do Newton's laws describe the motion of an object?

Newton's First Law (Law of Inertia)

• An object at rest stays at rest

• Object in motion stays in motion, unless acted on by an unbalanced force

• This is why rollercoasters & cars have seatbelts. If the car or roller coaster makes a sudden stop, your body will continue moving unless another force stops it. Seatbelts provide that force.

Newton's Second Law

• Total net force acting on an object is equal to mass times acceleration

• F=m*a

• Force measured in Newtons or kg x m/s², mass is measured in kg, acceleration is measured in m/s²

• To convert g → kg = divide g by 1000

Three alternative ways to use the formula:

Newton's Third Law of Motion

• States that for every action, there is an equal and opposite reaction

• Action and reaction forces

• Example: Rocket's engines push on those gases (action force), and the gases push back (reaction force). The reaction pushes the rocket off the ground.

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What's Due Today and Tomorrow

• Today: Gravity Quiz & start Newton's Laws of Motion: Warm-up, Instruction, Summary, and Assignment 1

• Tomorrow: Newton's Laws of Motion: Assignment 2 & Quiz