Integrated Science – 9 Chapter 4 The Laws of Motion Integrated Science – 9 Chapter 4

The First Two Laws of Motion Section 1

Newton’s Laws of Motion When you lift a backpack, you exert a force on an object and cause it to move. The backpack was initially at rest. The force applied caused the velocity to change. If I push down on my book on the desk, does it move? How are forces and motion related? Sir Isaac Newton explained this relationship with three rules of motion.

The First Law of Motion Newton’s First Law of Motion describes how an object moves when the net force is zero. Are these objects at rest?

The First Law of Motion The First Law of Motion: If the net force acting on an object is zero, the object remains at rest. Or, if the object is moving, it continues moving in a straight line with constant speed. In other words, if all forced are balanced, the velocity of an object doesn’t change.

Inertia and Mass All objects have a property called inertia. INERTIA is the tendency of an object to resist a change in its motion. Mass influences an object’s inertia The greater an object’s mass, the greater it’s inertia. How would this relationship look in a line graph?

Inertia and the First Law The First Law of Motion says an object in motion will remain in motion. Inertia says that an object will resist a change in motion unless acted on by another force. The First Law of Motion is often called the law of inertia.

The Second Law of Motion The Second Law of Motion describes the relationship between force, mass, and acceleration. Both increased mass and increased acceleration will caused an increase in force.

The Second Law of Motion The Second Law of Motion states that the acceleration on an object is in the same direction as the net force on the object, and that the acceleration can be calculated by the following equation: acceleration (a) = net force (Fnet) mass(m)

Calculating Net Force The formula given in the second law can be rearranged to state: F = m x a F= force m= mass a = acceleration

Example A tennis player hits a ball, the ball changes velocity over a short period of time and the ball’s acceleration could be as high as 5,000 m/s2 The ball’s mass of 0.06 kg, so the net force exerted on the ball would be: F net = (0.06 kg) x (5000 m/s2) = 300 kg m/s2 = 300 N

Car Crashes http://www.youtube.com/watch?v=yUpiV2I_IRI