Download Notes for Newton

I
Dynamics – Study of the causes of Motion.
A. Forces – A force is a push or pull that may cause a change in motion
1. Forces are vector quantities that have a magnitude and a direction
2. Units for Force is the Newton = (kg)(m)/s2
B. Types of Forces
1. Contact Forces – forces that require contact
2. Field Forces – Forces where contact is not necessary (gravity and EM)
C. Four Fundamental Forces of Nature
1. Gravity (weakest but works over great distances)
2. Weak Nuclear Force
3. Electromagnetic Force
4. Strong Nuclear Force (holds protons in the nucleus together)
II
Newton’s 3 Laws of Motion
A. Newton’s First Law
1. An object in motion will remain in motion, an object at rest will remain at rest unless
acted on by an outside force.
2. Inertia – a measure of the resistance to change motion
i. Dependant on mass – as mass increases, inertia increases
ii. Independent of Velocity
3. Equilibrium – When the sum of the forces acting on an object equal zero.
a. Object in equilibrium are either moving at constant velocity or are at rest
B. Newton’s Second Law
1. The acceleration of an object is directly proportional to the net external force acting
on the object and inversely proportional to the object’s mass (Fnet = ma)
2. If an net force or unbalanced force exists acceleration will occur (constant force
produces uniform acceleration)
3. The sign of the force must agree with the sign of the acceleration
4. A single force acting on an object is unbalanced, must be accelerating
5. On a D-T graph the slope = velocity (constant velocity is direct relationship)
6. On a D-T graph a curved line indicates acceleration (unbalanced force)
7. On a V-T graph an object in equilibrium has constant velocity (horizontal line)
C. Newton’s Third Law
1. For every action there is an equal and opposite reaction. (forces come in pairs)
2. Examples – you kick a wall, the wall kicks you.
3. Recoil – a bullet is fired from a gun and the bullet accelerates at a high speed, the
bullet also pushes the gun back with an equal force but unequal masses and
accelerations.
4. Example a 5 kg handgun fires and causes a 10 gram bullet to accelerate at 100 m/s
east, calculate the acceleration of the handgun. {a=0.2 m/s2 west}