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!
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