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!