Force and Motion Gravity and Motion Which would

Force and Motion

Gravity and Motion • Which would hit the ground first, a soccer ball or a bowling ball?

400 B. C. in Greece - Aristotle “the rate at which an object falls depends on the object’s mass” Philosopher so he never tested his idea

1500 s in Italy – Galileo Galilei “mass of an object does not affect the time the object takes to fall to the ground”

Gravity and Motion • Which would hit the ground first, a soccer ball or a bowling ball?

They would both hit at the same time! WHY?

Gravity causes all objects to accelerate toward the Earth at a rate of 9. 8 m/s²

You can calculate the change in velocity of a falling object… Equation: Δv = g x t

Δv = g x t • Δv = change in velocity • g = acceleration due to gravity (9. 8 m/s²) • t = time

Practice - Δv = g x t • A penny is dropped from the top of a tall stairwell. What is the penny’s velocity after it has fallen 2 seconds?

Practice - Δv = g x t • The same penny hits the ground in 4. 5 s. What is the penny’s velocity as it hits the ground?

Practice - Δv = g x t • A marble is dropped from a tall building. The marble hits the ground with a velocity of 98 m/s downward. How long was the marble in the air?

Practice - Δv = g x t • An acorn falls from an oak tree. It hits the ground with a velocity of 14. 7 m/s downward. How long did it take the acorn to land?

If different masses can fall at the same time, same masses definitely should!

Air Resistance – force that opposes the motion of objects through air Depends on: Size, Shape, and Speed of the object

As speed increases, so does air resistance • It continues to increase until it is equal to the downward force of gravity Gravity Force Air Resistance

Terminal velocity • when the object stops accelerating because air resistance equals gravity Gravity Force Air Resistance

Terminal velocity can be a good thing • Normal terminal velocity is 5 – 40 m/s • Without air resistance, they could reach velocities near 350 m/s

Penny Dropped from Empire State Building Reach Speeds to Kill? • http: //www. youtube. com/watch? v=PHxv. MLo KRWg

Free Fall

• Free fall – if only gravity and no other forces are acting on it; no place with air So where can free fall occur?

Freefall can occur: • In a vacuum • In space

In a vacuum • http: //isites. harvard. edu/icb. do? keyword= k 16940&pageid=icb. page 197826&page. Conten t. Id=icb. pagecontent 388782&view=watch. do& view. Param_entry=59768&state=maximize#a_ icb_pagecontent 388782

In Space • https: //www. youtube. com/watch? v=KDp 1 ti. U s. Zw 8

Why is the astronaut floating inside the space shuttle? weightless?

Orbiting • when an object travels around another object in space

Orbit • Caused by moving forward and free falling

Projectile Motion – curved path an object follows when thrown near the surface of the earth Horizontal motion + Vertical motion Curved path

Projectile Motion

Projectile Motion

Projectile Motion

Projectile Motion

Projectile Motion

• horizontal motion – parallel to the ground • vertical motion – perpendicular to the ground

They are independent of each other! • gravity affects only the vertical motion

Why is this important to know?

Projectile Design!!! • You will be working in groups of 5 • Create a device that will project a marble into a container 1 meter away • You will design your device and bring any items needed to make it to class tomorrow. • You will want to test it out several times and make sure it is accurate – you each get 2 shots in front of the class!

Ideas?