1. Newton’s 2nd Law – Force and mass determine accleration

2. Isaac Newton An object in motion will stay in motion.
An object at rest will stay at rest.
Unless acted upon by another force.
2) The greater the force the greater the acceleration.
F=ma
3) For every action there is an equal and opposite reaction

3. Newton’s second law relates force, mass, and acceleration.
“The greater the force the greater the acceleration. F=ma” – Newton’s Second Law
The key points of Newton’s second law are that the acceleration of an object is:
- Directly proportional to the force acting on the object
- Inversely proportional to the mass of the object
- In the same direction as the net force acting on the object
Newton’s second law is summed up by the equation
Force = mass X acceleration or F=ma.
Force : F=ma
Mass: m=F/a
Acceleration: a=F/m

4. Sample Problem - Calculating Mass
Newton’s second law is summed up by the equation
Force = mass X acceleration or F=ma.
Force : F=ma
Mass: m=F/a
Acceleration: a=F/m
A rocket man is accelerating at 2 m/s2. The force on it is 1 N (Newton). What is the mass of the rocket man?
Mass: m=F/a
2 m/s2 F
acceleration = 2 m/s2
m = a
1 N
m =
1 N
2 m/s2
Force = 1 N X
1 kg X m/s2 .5
m =
2)1.00
1 N = 1 kg X m/s2
1 kg X m/s2 X
2 m/s2
-10
m = .5 kg

5. Sample Problem #2 - Calculating Force
Newton’s second law is summed up by the equation
Force = mass X acceleration or F=ma.
Force : F=ma
Mass: m=F/a
Acceleration: a=F/m
Two sumo wrestlers face off. The wrestler on the left has a mass of 130 kg and accelerates at a rate of 1 m/s2. The wrestler on the right has a mass of 30 kg and accelerates at a rate of 32 m/s2. Who will generate more force and push his opponent outside the circle?
Force : F=ma

6. Sample Problem #2 - Calculating Force
F=ma
F=ma
F = 130 X 1
F = 30 X 32
F = 130 N
F = 960 N
130 N
960 N
m= 130 kg
a= 1 m/s2
m= 30 kg
a= 32 m/s2

7. Forces can change the direction of motion.
Forces can change the direction of an object without changing its speed if the force acts at right angles to the motion.
A force that continuously acts at right angles to an objects motion will pull the object into circular motion.
Any force that keeps an object moving in a circle at a constant speed is called a centripetal force.
The centripetal force needed to keep an object moving in a circle depends on:
- The mass of the object
- The speed of the object
- The radius of the circle
centripetal force =
(mass X speed2)
radius