gravity and motion. galileo’s story gravity and acceleration objects fall to the ground at the...

Gravity and Motion

Galileo’s Story

Gravity and Acceleration• Objects fall to the ground at the same rate

because the acceleration due to gravity is the same for all objects

• What is acceleration?– The rate at which the velocity(speed)

changes over time

• All object accelerate towards the Earth at a rate of 9.8 m/s per second. – Example: You drop a penny off the top of a

building. It’s starting velocity is 0 m/s. After one second, the velocity has increased to 9.8 m/s. After two seconds, the velocity is 19.6 m/s.

Free Fall

• Free Fall occurs when the only force acting on an object is gravity.

• In Free Fall, the force of gravity is an unbalanced force, which causes the object to accelerate.

Video Time!

Penny Drop!

If a penny is dropped from a high enough building, can it seriously injure a person below?

Solving Problems with Free Fall

yy

y = 0.5gt2

yy

Calculate heightA stone is dropped down a well and it takes 1.6 seconds to reach the bottom. The acceleration due to gravity is 9.8 m/s2

How deep is the well? You may assume the initial speed of the stone is zero. • G: g = 9.8 m/s2 t=1.6 seconds

• U: y

• E: y = 0.5gt2

• S: y = 0.5 (9.8m/s2) (1.6)2

• S: 12.54 meters

Your turn! Solve the problem below!A stone tumbles into a mineshaft and strikes bottom after falling 6.1 seconds. How deep is the mineshaft? (Assume gravity = 9.8 m/s2)

• G:

• U:

• E: y = 0.5gt2

• S:

• S:

Solving for velocity: v = v0 + gtHow fast will a pebble be traveling 3 seconds after being dropped? Assume the initial velocity is 0m/s and the acceleration of gravity is 9.8 m/s2.

• G: g= 9.8 m/s2 t= 3s vo= 0m/s

• U: v

• E: v = v0 + gt

• S: v = 0m/s + (9.8m/s2)(3s)

• S: v= 29.4 m/s

Your turn! Solve the Problem below!A penny dropped into a wishing well reaches the bottom in 2.5 seconds. What was the velocity at impact? Assume the initial velocity is 0m/s and the acceleration of gravity is 9.8 m/s2. • G:

• U:

• E: v = v0 + gt

• S:

• S:

Air Resistance and Mass

• The acceleration due to gravity does not depend on the mass of the object which is falling.

• However, we know that is not always the case.

•RIGHT?

Air resistance

• A type of fluid friction that acts on falling objects.• It is an upward force exerted on all objects.• Falling objects with greater surface area

encounter more air resistance.

• Which encounters more air resistance…crumpled paper or flat paper?

• Which one falls faster?

Terminal Velocity

• Air resistance increases as a falling object’s speed increases.

• Eventually, the rate of acceleration is reduced to zero and the object falls with constant speed.

• The maximum speed at which an object falls when limited by air resistance is called the terminal velocity.

It’s Raining Paper, Bananas, and Free Body Diagrams.

Projectile Motion

• Projectile motion is the curved path an object follows when it is thrown or propelled near the surface of the Earth.

• Projectile motion has two components– Horizontal motion– Vertical motion

Projectile Motion

What do you need to consider when playing darts?

That’s a wrap for Forces!