Forces in Motion Chapter 2 Mrs. Estevez

Gravity and Motion What happens when you drop a baseball and a marble at the same time? What happens when you drop a baseball and a marble at the same time? Predict what will happen when both objects are dropped at the same time from the same height. Predict what will happen when both objects are dropped at the same time from the same height.

Gravity and Motion Galileo Galilei- the mass of an object DOES NOT affect the time it takes an object to fall to the ground. Galileo Galilei- the mass of an object DOES NOT affect the time it takes an object to fall to the ground. Acceleration due to gravity is the same on all objects: Acceleration due to gravity is the same on all objects: 9.8 m/s² 9.8 m/s²

Acceleration at a Constant Rate All objects accelerate towards earth at a rate of 9.8 m/s/s. All objects accelerate towards earth at a rate of 9.8 m/s/s. Every second that the object falls the object increases its velocity by 9.8m/s/s. Every second that the object falls the object increases its velocity by 9.8m/s/s. Change in velocity of falling objects can be calculated: Change in velocity of falling objects can be calculated: Change in Velocity= Change in Velocity= ( 9.8m/s/s) x (time it takes object to fall.) ( 9.8m/s/s) x (time it takes object to fall.)

Velocity of Falling Objects A boy standing on a high cliff dives into the ocean below and strikes the water after 3 seconds. A boy standing on a high cliff dives into the ocean below and strikes the water after 3 seconds. What is the boys velocity? What is the boys velocity? (29.4 m/s/s) (29.4 m/s/s) A rock falls from a high cliff and hits the ground in 6.5 seconds. What is its final velocity? A rock falls from a high cliff and hits the ground in 6.5 seconds. What is its final velocity? (63.7 m/s/s) (63.7 m/s/s)

Gravity and Motion Try dropping a crumbled piece of paper and a flat piece of paper. Try dropping a crumbled piece of paper and a flat piece of paper. Why does this contradict what we just learned? Why does this contradict what we just learned?

Air Resistance Air resistance- the force that opposes the motion of objects through air. Air resistance- the force that opposes the motion of objects through air. Depends on size, shape, and speed. Depends on size, shape, and speed.

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Terminal Velocity As an object falls: As an object falls: –The speed of the object increases and the air resistance increases. –The upward force of the air increases until it equals the downward force o the gravity (0 N) –The object stops accelerating. –It falls at a constant velocity- TERMINAL VELOCITY

Free Fall Only happens when gravity is the only force acting on the object. Only happens when gravity is the only force acting on the object. Can only occur where there is no air. Can only occur where there is no air. –Space (ex. Floating astronauts) –Vacuum (a place where there is no matter)

Projectile Motion The curved path an object follows when it is propelled or thrown near the surface of the earth. The curved path an object follows when it is propelled or thrown near the surface of the earth. –Horizontal motion (force on the object) – Vertical Motion (gravity pulls it down)

Newton’s Laws First Law – Inertia Second Law – Acceleration, Force & Mass Third Law – Action-Reaction

First Law Inertia –An object at rest [not moving] remains at rest unless acted on by a force [push or pull] –An object in motion remains in motion unless acted on by a force [push or pull]

First Law Inertia & Mass –Mass is the amount of matter in an object –The more MASS an object has, the more INERTIA the object has. –Bigger objects are harder to start & stop

Second Law Acceleration & Mass Definitions –Acceleration is a change in velocity [speed or direction] –Mass is the amount of matter in an object

Second Law Acceleration & Force –The more force placed on an object, the more it will accelerate [change its motion] Acceleration & Mass –The more mass [or inertia] an object has, the more force it takes to accelerate the object

Third Law Action – Reaction –Forces are always produced in pairs with opposite directions & equal strengths –For every force there is an equal and opposite force

The truck is in motion. What is the force that causes it to stop? The push of the stopped car. The car is at rest. What is the force that causes it to move? The push of the truck.

What about the ladder on top of the truck? The ladder is in motion because the truck is in motion. When the truck stops, the ladder stays in motion. The truck is stopped by the force of the car, but the ladder is not. What force stops the ladder? Gravity.

The truck is in motion, the car is at rest. How do each of these vehicles accelerate? The truck stops moving. The car starts moving. Which one will be the hardest to accelerate? The truck because it has the most mass.

Why does the car move [accelerate] when it is hit by the truck? The heavy and moving truck has more force than the small, at rest car. Why does the truck stop moving when it hits the car? The force of the car pushing back on the truck, plus the force of friction between the massive truck and the road slow down, the stop the truck.

The truck hits the car. An action force stops the truck. What is the equal and opposite reaction force? The force that pushes the car forward.

Momentum Depends on mass and velocity. Depends on mass and velocity. The more momentum, the harder it is for an object to stop or change direction. The more momentum, the harder it is for an object to stop or change direction. Calculating momentum: p = m x v Calculating momentum: p = m x v p = momentum p = momentum m = mass m = mass v = velocity v = velocity

The Law of Conservation of Momentum States that any time objects collide, the total amount of momentum stays the same. States that any time objects collide, the total amount of momentum stays the same. Newton’s 3 rd Law Newton’s 3 rd Law