physics lecture 01/27

Understanding Forces

• Forces are usually classified into two categories: static and kinetic forces.

  • Static forces are in place when objects are at rest.

  • Kinetic forces come into play when objects are in motion.

Effects of Ice on Braking

• When you hit an icy surface while driving, the forces acting on the vehicle change significantly.

  • Upon hitting ice, braking leads to static friction turning into kinetic friction, which may cause wheels to lock up.

  • Locked brakes potentially lead to skidding.

Acceleration of Objects

• To analyze the motion of an object, you start with understanding acceleration.

  • Determining acceleration of an object (e.g., a ball) involves breaking down the problem into steps.

Setting Up the Problem

1. Draw a Free Body Diagram (FBD)

   • An FBD is essential for visualizing all forces acting on the object.

   • Example: When considering gravitational effects, the force acting downward is the weight (mg).

2. Identify Forces

   • Recognize that gravitational pull is a continuous force, affecting an object even when analyzing other forces.

3. Establish a Coordinate System

   • Define a coordinate system to analyze forces effectively, typically using a plus or minus notation for direction.

Analyzing Forces in Context

• The overall approach to solving force problems can be summarized as follows:

  • Write down the sum of the forces in the identified direction(s).

  • For gravitational force:

    • Usually expressed as (-mg), where (m) is mass and (g) is the acceleration due to gravity.

  • Incorporate any other forces like normal force into the equation to establish balance.

Normal Force and Scale Interaction

• Understand the role of normal force:

  • The normal force is the reaction force exerted by a surface to support the weight of an object resting on it.

  • When standing on a scale:

    • The normal force acting on the scale supports your weight (mg) plus any additional vertical forces affecting you.

    • When stationary, the normal force equals the weight force.