NEWTON’S 2 nd Law of Motion. Newton’s 2 nd law of Motion Describes the relationship of how something with a mass accelerates when it is pushed/pulled.

NEWTON’S 2NEWTON’S 2ndnd Law Law of Motionof Motion

Newton’s 2Newton’s 2ndnd law of law of MotionMotion

Describes the relationship of how something with a mass Describes the relationship of how something with a mass accelerates when it is pushed/pulled by a force.accelerates when it is pushed/pulled by a force.

Force

Acceleration

Newton’s 2Newton’s 2ndnd law of law of MotionMotion

An object will accelerate in the direction of a net An object will accelerate in the direction of a net force.force.

Force

Acceleration

Is the direction of the Is the direction of the motion of the object always motion of the object always the same as the direction the same as the direction of the acceleration?of the acceleration?

1 2

50%50%

1.1. YesYes

2.2. NoNo

F = maF = maNet Force

mass

acceleration

F= ma Song

UnitsUnits

F = mF = m··aa = kg= kg·m/s·m/s22

= Newton= Newton

ExampleExample For a while, the National For a while, the National

Marbles Tournament was, Marbles Tournament was, as one newspaper put it in as one newspaper put it in 1925, "1925, "the highest honor the highest honor possible in the sporting possible in the sporting world for (kids).” world for (kids).” The game The game of marbles was a highly of marbles was a highly competitive game from the competitive game from the early 1900’s to late 1960’s in early 1900’s to late 1960’s in the United States.the United States.

The game of marbles was The game of marbles was played by propelling a played by propelling a marble with the thumb to hit marble with the thumb to hit another marble as to drive it another marble as to drive it out of a circle.out of a circle.

1950 VFW National ChampTilton "Pork Chop" Holt inaction at the Eaton Rapids,Michigan finals. From LIFEMagazine, June 26, 1950

Example (cont.)Example (cont.)

““Pork Chop” Holt flicks .036 kg marble at Pork Chop” Holt flicks .036 kg marble at an acceleration of 7.2 m/san acceleration of 7.2 m/s22. What force . What force did he use to propel his marble?did he use to propel his marble?

EXAMPLEEXAMPLE The Inuit people of the Arctic The Inuit people of the Arctic

region, one of the most region, one of the most forbidding territories on forbidding territories on Earth, have an economy that Earth, have an economy that revolves around the revolves around the changing seasons and the changing seasons and the animals that could be animals that could be successfully hunted during successfully hunted during these periods. Assume an these periods. Assume an that an Inuit has caught a that an Inuit has caught a sled full of salmon. If he sled full of salmon. If he pulls the sled with a force of pulls the sled with a force of 80 N and the sled has a 80 N and the sled has a mass of 87kg, what is the mass of 87kg, what is the acceleration of the sled as acceleration of the sled as he pulls it a short distance he pulls it a short distance across the snow?across the snow?

ExampleExample

A 15 kg object is being pulled upwards by a A 15 kg object is being pulled upwards by a force of 3 N and to the left by 4 N. What is the force of 3 N and to the left by 4 N. What is the objects acceleration?objects acceleration?

a = ?a = ?m = 15 kgm = 15 kgFFnetnet = 5 N = 5 N

4 N

3 N

a = Fnet / m

= 5 N / 15 kg

= 0.33 m/s2

Application of Newton’s Application of Newton’s 22ndnd Law: Weight & mass Law: Weight & mass

Does your mass change Does your mass change on the moon?on the moon?

1 2

50%50%

1.1. YesYes

2.2. NoNo

How would the size of these forces change on the moon?

How would the size of these forces change on the moon?

WHY?

What things affect weight?

AND

Fw = mg

Weight (N)

Acceleration caused by gravity

(m/s2)

Mass (kg)

What’s your mass?What’s your mass?

Convert pounds into kilograms.Convert pounds into kilograms.

What’s your weight in What’s your weight in Newtons (on the EARTH)?Newtons (on the EARTH)?

9.8 m/s9.8 m/s22

FFww = mg = mg

Calculate the following using your information:

mass = ____ kg

weight = ____ lbs

weight = ____ N mass = ____ kg

weight = ____ lbs

weight = ____ N

mass = ____ kg

weight = ____ lbs

weight = ____ N

Earth JupiterMoon

g = 9.8 m/s2 g = 1.6 m/s2 g = 26 m/s2

How does this apply to How does this apply to falling objects?falling objects?

A closer look at free-fallA closer look at free-fall(WITH AIR RESISTANCE)(WITH AIR RESISTANCE)

m = 100 kg

Weight

Air resistance If force due to air resistance was 400 N, what is the object’s acceleration?

What is happening to the What is happening to the speed of the previous speed of the previous object?object?

1 2 3

33% 33%33%

1.1. It is speeding upIt is speeding up

2.2. It is slowing downIt is slowing down

3.3. It is staying the same.It is staying the same.

Terminal VelocityTerminal Velocity

When an object in free-fall is no longer When an object in free-fall is no longer acceleratingaccelerating

m = 100 kg

Air resistance

Weight

A challenge!A challenge!

What is the force?What is the force?

If I drag my book across the table with a 3 N If I drag my book across the table with a 3 N force at a CONSTANT VELOCITY, what is force at a CONSTANT VELOCITY, what is the force of friction?the force of friction?

Force pulling = 3 NForce pulling = 3 NForce of friction = ?Force of friction = ?

a =

Fnet =

What is the force?What is the force?

If I drag my 1.5 kg book across the table with a If I drag my 1.5 kg book across the table with a 3 N force and it accelerates at a rate of 3 N force and it accelerates at a rate of 1.1 m/s1.1 m/s22, what is the force of friction?, what is the force of friction?

Force pulling = 3 NForce pulling = 3 NForce of friction = ?Force of friction = ?

a = 1.1 m/s2

Fnet =

1.5 kg