What would happen if you jumped into a well that went all the way through Earth?

See answer in video

Newton’s 2nd Law of Motion (F=ma) describes

falling and weight

F=maunits

• F = force– Measured in newtons (N)

• m = mass– Measured in kilograms (kg)

• a = acceleration– Measured in meters per second

per second (m/s)

What is acceleration

?

• acceleration = change in velocity over time

a = or a =

Thinking about

the law

• If the force acting on an object goes down, and the mass doesn’t change, how does the acceleration change?

Weight is applied

Newton’s 2nd

• Fg = mag

(or W=mg or F = mg)

– Fg = force due to gravity ( or W=weight)

– ag (or g) = acceleration due to gravity

• always = 9.8 m/s2 on Earth• Does a big guy or little guy fall

faster when bungee jumping?

Weight is applied

Newton’s 2nd

• Fg = mag

(or W=mg or F = mg)

– Fg = force due to gravity ( or W=weight)

– ag (or g) = acceleration due to gravity

• always = 9.8 m/s2 on Earth• Does a big guy or little guy fall

faster when bungee jumping?• They fall at the same speed,

as mass is irrelevant to freefall speed

Which would fall faster without air resistance, feathers or a bowling ball? video

Air Resistance and free-fall

• In air…– A stone falls faster than a

feather• Air resistance

affects stone less• In a vacuum

– A stone and a feather will fall at the same speed.

Free-fall utilizes “g”

The acceleration of gravity (g) for objects in free fall at the earth's surface is 9.8 m/s2. Galileo found that all things fall at the same rate.

Which would land first, a bullet fired or a bullet dropped?

• Each bullet shows its position at seconds 0, 1, 2,and 3

Free-fall

The rate of falling increases by 9.8 m/s every second.

Height = ½ gt2

(Height is abbreviated either “y” or “d”)

For example:

½ (9.8 )12 = 4.9 m

½(9.8)22 = 19.6 m½ (9.8)32 = 44.1 m½ (9.8)42 = 78.4 m

Free-fall

A ball thrown horizontally will fall at the same rate as a ball dropped directly.

Its velocity can be calculated by multiplying the time in seconds by “g”.

v=gt

Free-fall

A ball thrown into the air will slow down, stop, and then begin to fall with the acceleration due to gravity.

When it passes the thrower, it will be traveling at the same rate at which it was thrown.

Projectile motion path shape

An object thrown upward at an angle to the ground follows a curved path called a parabola.

What do you notice about this shape?

Air Resistance and free-fall– A person in free fall

reaches a terminal velocity of around 54 m/s (about 130 mi./hr.)

– With a parachute, terminal velocity is only 6.3 m/s

Allows for a safe landing

-the terminal velocity for a cat is 60 mi./hr.

Air Resistance• Ideal angle for a projectile

– In a vacuum, maximum distance is at an angle of 45o

– With air resistance (real world), angle is less• Baseball will go furthest hit at an angle of around 40o