Transcript 3.1 Newton`s 2nd Law

Newton’s Second Law
Physical Science 3.1
Force and Acceleration

Greater force = greater acceleration
Applying force causes change in velocity
 Velocity change over a shorter period of time =
more acceleration change
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Same force on different object may result in
different acceleration

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More mass = less acceleration
Newton’s 2nd law: The net force acting on an
object causes the object to accelerate in the
direction of the net force

a = F/m
Force and Acceleration

Units
Mass: kg
 Acceleration: m/s2
 Force: N = kg*m/s2

a = F/m also written as F = ma
 Friction: The force that opposes motion
between two surfaces that are touching each
other
 2 Factors influencing amount of friction

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Kinds of surfaces and the force pressing the
surfaces together
Friction
Surfaces of objects are rough
microscopically
 Cause of friction: microwelds- when
highest bumps from each surface stick
together
 Stronger forces pushing surfaces together
= stronger microwelds
 Static friction: - the friction between two
surfaces that are not moving past each
other

Friction

Sliding friction- the reason you must continue
to apply force after starting motion
Acts against your push
 Microwelds constantly break and reform

Lack of friction = lack of motion for us and
vehicles
 Rolling friction- Friction between rolling
object and surface- due to microwelds
between wheel and surface it rolls over

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Weakest form of friction
Air Resistance
On earth- feather falls slower than tennis ball
due to air resistance
 Air resistance- force acting opposite to
motion of falling object

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Depends on Speed, size, and shape of falling
object
In vacuum (no air) - feather and tennis ball
fall at the same rate- no air resistance
 Terminal velocity- highest velocity a falling
object can reach

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When the forces on a falling object are balanced