LAWS OF MOTION

Newton

’

s First Law

   an object at rest remains at rest and an object in motion maintains its velocity (stays in motion) unless it experiences an unbalanced force (outside force).

Aka Law of Inertia

INERTIA

     tendency of an object to resist being moved or if object is moving, resist a change in speed or direction until an outside force acts on object.

All objects resist changes in motion Less mass, less inertia More mass, more inertia

Chapter 11

INERTIA EXAMPLE

 Seat belts and car seats provide protection.

• Because of inertia, you slide toward the side of a car when the driver makes a sharp turn.

• When the car you are riding in comes to a stop, your seat belt and the friction between you and the seat stop your forward motion.

WHY WEAR A SEATBELT?

SEATBELT IN THE BACKSEAT?

Newton

’

s Second Law

 unbalanced force acting on an object equals object ’ s mass times its acceleration.

 Force = mass 

acceleration

SI Unit:   newtons (N) 1 N = 1 kg  1 m/s 2

F m a

Zookeepers lift a stretcher that holds a sedated lion. The total mass of the lion and stretcher is 175 kg, and the lion’s upward acceleration is 0.657 m/s stretcher?

2 . What is the unbalanced force necessary to produce this acceleration of the lion and the GIVEN: WORK : F = ?

F = ma m= 175 kg a = 0.657 m/s 2 F = (175 kg) (0.657 m/s 2 ) F = 115 N

m F a

What is the net force necessary for a 1.6 x 10 3 kg automobile to accelerate forward at 2.0 m/s 2 ?

GIVEN: F = ?

m= 1.6 x 10 3 kg a = 2.0 m/s 2

m F a

WORK : F = ma F = (1.6 x 10 3 kg) (2.0 m/s 2 ) F = 3.2 x 10 3 N

A baseball accelerates downward at 9.8 m/s baseball’s mass?

2 . If the gravitational force is the only force acting on the baseball and is 1.4 N, what is the GIVEN: F = 1.4 N m= ?

a = 9.8 m/s 2

F m a

WORK : m = F/a m = 1.4 N / 9.8 m/s 2 m = 0.14 kg

A sailboat and its crew have a combined mass of 655 kg. Ignoring frictional forces, if the sailboat experiences a net force of 895 N pushing it forward, what is the sailboat’s acceleration?

GIVEN: F = 895 N m= 655 kg a = ?

m F a

WORK : a = F/m a = 895 N / 655 kg a = 1.37 m/s 2