newton’s first and second laws of motion

Key Concepts•What is Newton’s first law of motion?

•What is Newton’s second law of motion?

Key Terms - Inertia

An object at rest will remain at rest, and an object moving at a constant velocity will continue moving at a constant velocity, unless acted upon by an unbalanced force

Clothes on the floor will stay there unless someone uses a force to pick them up

A tennis ball that was hit will continue until a force stops it

Gravity and friction are the 2 forces on Earth that often change an object’s motion

Tendency of an object to resist a change in motion

Newton’s first law is also called the Law of Inertia

Example – a person continues to move forward when a car stops

The greater the mass of an object, the greater the inertia

The greater the inertia, the greater the force needed to move the object, and the greater the force needed to change its motion

Acceleration depends on the object’s mass and the net force acting on the object

Acceleration = Net Force Mass Force = mass *

acceleration Units = Newton (N) = kg

*m/s2

Calculating Force: A speedboat pulls a 55kg water skier. The force causes the skier to accelerate at 2.0m/s2. Calculate the net force that causes this acceleration.

Information given: ◦ Mass of water skier =55kg◦ Acceleration of water skier= 2.0 m/s2

What quantity are you trying to calculate?◦ Net force Fnet

What formula should you use? A = fnet or Fnet = m*a m Perform calculation – 55kg *2.0m/s2 = 110kg*m/s2

= 110N

What is the net force on a 1,000 kg object accelerating at 3 m/s2?

Remember Fnet= m * a

What net force is needed to accelerate a 25 kg cart at 14m/s2? F= m* a

If you keep the mass constant, a change in force will have the same change in the acceleration

If you keep the force constant, an increase in mass will cause a decrease in acceleration

Opposite is also true – If the force is constant, a decrease in mass will cause an increase in acceleration

http://www.physicsclassroom.com/class/newtlaws/u2l1b.cfm

http://www.rcs.k12.va.us/csjh/sieber/PhysicalSci_1stSem.htm