Year 10 Term 2 - Class Notes

Acceleration

• Acceleration = rate of change of velocity; it is a vector quantity (direction is involved).
• Units – m/s 2

Where a = acceleration (m/s s) v 1 = initial velocity (m/s) v 2 = final velocity (m/s) t = time (s)

Note

• If an object is slowing down (decreasing velocity) then a is negative.

• If an object is speeding up (increasing velocity) then a is positive.

Vertical motion (ignoring air resistance)

• If an object is free-falling then a = + 9.8 m/s²

• If an object is thrown vertically upwards then a = -9.8 m/s²

Note from Newton ’s Second Law F = ma

a = F/m

where a = acceleration in m/s ², F = unbalanced net force in N, m = mass in kg.

For calculations involving vertical motion we will ignore air resistance.

However, w hen objects that fall from great heights they may reach terminal velocity – As the object falls faster, air resistance (drag) increases until it eventually equals the downward gravitational force and the object now moves at constant velocity. The forces are now balanced.