Newton's 2nd and 3rd Law

1. Newton’s 2nd Law of Motion
“The force on an object is directly proportional to the product of
its mass and acceleration.”
Newtons 2nd law connects the mass of an object, how much force is applied to it and
how fast it accelerates/decelerates.

2. Newton’s 2nd Law of Motion
• If I push a car with 50N of force and it accelerates at 5m/s,
does that mean that if I push on a truck with the same force, it
too will accelerate at 5m/s?

3. Newton’s 2nd Law of Motion
F = ma
(i.e. Force = mass  acceleration)
or
m
F
a 
a
F
m 

4. Fa (Constant m)
Fm (Constant a)
a1/m (Constant F)
Force is proportional to acceleration.
This means if one increases, so too does the other.
If I push harder, I would expect it to accelerate more.
Force is proportional to mass.
This means if one increases, so too does the other.
If I increase the mass of the object, I would expect to need more force to make it move.
Acceleration is inversely proportional to mass.
This means if one increases, the other decreases.
If I make a car lighter, I would expect it to accelerate faster. This is why the mass of racing cars is so important.

5. Newton’s 3rd Law of Motion
“Every action has an equal and opposite reaction.”

6. • The cannon exerts a force on the cannonball.
• The cannonball exerts a force on the cannon.
This means if object A is pushed with a force of 5N, it pushes back with 5N.
• Chuck Norris punches you in the face.
• Your faces punches chuck Norris’ fist!

7. Newton’s 2nd law explained

8. For your viewing pleasure….or torment

9. Mind Blower
• If you jump off the ground, you are pushing yourself away from the
earth, which means the earth is also pushing itself away from you.
So when you jump you should push the earth off its axis right?
Person excerts force against earth:
Mperson = 80kg
Acceleration = 3ms-2
F = m x a = 240N
Earth excerts force against person:
Equal force = 240N
Mearth = 5.972x1025 kg
Therefor aearth=f/m
aearth = 4.01x10-23 ms-2

10. This is exactly why you feel recoil when firing a gun.
So if a gun produces 600N of force when you pull the trigger, why doesn’t it shoot the gun
backwards at a high speed like the bullet?
Answer: Newtons second law - the masses are different. Same force, different mass =
different acceleration.