Newton’s 2nd Law

Force and Acceleration• Forces cause

acceleration. • Acceleration is

directly proportional to the net force acting on an object.

• The equation that expresses this is

• F=ma. • F=Force, m=mass,

a=acceleration

• Newton’s second law states that “the acceleration produced by a net force on an object is directly proportional to the magnitude of the net force, is in the same direction as the net force and is inversely proportional to the mass of the object”.

What are the units for force?

• The unit for force is the Newton (N).

• The Newton is actually 1kg-m/s2

• 1kg = 9.8N• 1lb = 4.45 N• 1kg = 2.2 lbs.

What is friction?

• Friction is a force that acts between bodies that are in contact with one another. The friction is a resisting force that is mainly due to irregularities in the two forces.

Overcoming friction

• When one object slides against another, it must either rise over the irregular bumps or scrape them off. Both ways require force.

• What is the net force? Why is there no acceleration?

Is there friction in fluids?

• Friction occurs in fluids (liquids and gases) also. Fluid friction occurs as an object pushes aside the fluid it is moving through.

Air resistance is a type of friction

• Air resistance is a type of fluid friction that sometimes equals the downward weight of an object.

• The result is no acceleration or a constant velocity.

• Why doesn’t the elephant’s acceleration change?

• Why does the mouse’s?

What is pressure?

• Pressure is defined as the amount of force divided by the surface area.

• The equation is : P = F/a• The metric unit is the

Pascal (Pa) or the N/m2.

• The common unit is the PSI (lbs/in2)

• Famous French scientist and mathematician – Blaise Pascal at right.

• Same weight, more pressure

• There is more pressure on the ground with high heels than with flat soles even though the weight is the same.

Why is “g” the same for all objects?

• An object with ten times the mass is pulled down by gravity with a force ten times as great and both will experience identical acceleration(9.8 m/s2)

• f/m = F/M