## Chapter 4 Summary

• Newton's Second Law states that the acceleration of an object is directly proportional to the Net Force applied to it and inversely proportional to its mass. This is commonly written as a = ΣF/m or, more commonly ΣF = ma.

• Weight is a force. It always acts downward and it is calculated by taking the object's mass (in Kg) and multiplying it by the acceleration due to gravity (g, in m/s/s).

• The reason why all objects accelerate downward at the same rate can be explained by Newton's Second Law. A large object has a lot of mass and also a lot of weight. A small object has less mass and less weight. The ratio between weight and mass, however is the same for both:

F/m = a = F/m

• By using Free Body Diagrams to find the net force on an object, the acceleration of the object can be calculated.

• Pressure is Force being applied over some Area.

• Newton's Third Law states that when two objects exert force on each other (either by contact or over a distance), the forces are equal in magnitude and opposite in direction. Forces always come in pairs.

• When two objects collide, the force felt by each object is the same. The resulting acceleration of the object depends on the object's mass.

ma = F = ma

• Friction

• Friction is

• To change directions, a centripetal force is applied to an object.

• ΣF = ma

• Weight = mg

• Pressure = Force / Area ( P = F/A)

• Weight is a force. It always acts downward and it is calculated by taking the object's mass (in Kg) and multiplying it by the acceleration due to gravity (g, in m/s/s).

• The reason why all objects accelerate downward at the same rate can be explained by Newton's Second Law. A large object has a lot of mass and also a lot of weight. A small object has less mass and less weight. The ratio between weight and mass, however is the same for both:

F/m = a = F/m

• By using Free Body Diagrams to find the net force on an object, the acceleration of the object can be calculated.

• Pressure is Force being applied over some Area.

• Newton's Third Law states that when two objects exert force on each other (either by contact or over a distance), the forces are equal in magnitude and opposite in direction. Forces always come in pairs.

• When two objects collide, the force felt by each object is the same. The resulting acceleration of the object depends on the object's mass.

ma = F = ma

• Friction

__always__opposes the motion of an object.• Friction is

__always__parallel to the surface while the normal force is always perpendicular.• To change directions, a centripetal force is applied to an object.

**Equations**• ΣF = ma

• Weight = mg

• Pressure = Force / Area ( P = F/A)