physics chapter 4 dynamics

1st newton’s law of motion

newton’s first law of motion is that the object will continue in its state of rest or motion unless a resultant force acts on it

Resultant force (net force)

forces are balanced —> resultant force is zero

** resultant force can be negative if going in opp direction

** can be reprensented by:

• +/-

• left/right

• arrows

Balanced vs unbalanced forces

need to know if at rest or alreadly moving at first

Balanced vs unbalanced forces

Example

** action-reaction pair N3L

• object at rest continue starting at rest

• object in motionn continue moving at constant velocity

unbalanced forces and newton’s second law

** if no friction, than the object will continue travelling at constant velocity

describe the ways in which a force may change the motion of a body

Newton’s second law of motion

F=ma

if F is alreadly representing smt in the qn, use Fr to represent resultant force

Newton’s third law

newton’s third law of motion states that for every action, there is an equal and opposite reaction

examples of action reaction pairs

** use the same format as action to describe reaction force

Free body diagrams

f → frictional force

F→ force

Fr→ resultant force

** add subscripts and put a legend

**must draw vertical forces such as weight and normal unless otherwise stated

Effects of resistive forces on motion , friction

Example

positive and negative effects of friction

Reducing negative effects of friction

Reducing negative effects of friction

Enhancing positive effects of friction

using F=ma to explain constant speed

1. The applied force and the opposing force have the same magnitude

2. Thus, there is no resultant force

3. since F=ma, the object’s acclearation is equal to zero as mass cannot equal to zero

4. travel at constant speed

1. object travelling at constant speed

2. accleration is equal to zero

3. since F=ma, there is no resultant force

4. the applied force and the opposing force have the same magnitude

using F=ma to explain motion/acceleration

1. The force on the object increases/decreases

2. thus, the resultant force on the object increases/decreases

3. since F=ma, the object’s acceleration increases/decreases

reminders