Physics Chapter on Motion and Forces

Friction and Motion

• Friction prevents slipping during walking.
• A spring's stretch increases proportionally with the applied force.
• Forces can change an object's speed, direction, or shape.
• Skydivers fall due to gravity and air resistance.
• Force diagrams show forces acting on an object.

Free-Body Diagrams

• Leopard diagrams show gravity and normal forces.
• Constant speed with changes in direction (e.g., airplane) demonstrates unbalanced forces affecting direction, not speed.
• Zero displacement occurs when an object returns to its starting point.
• Balanced forces (e.g., book on a table) result in no movement.
• Resultant forces are calculated by subtracting opposing forces.
• Unbalanced forces cause motion (e.g., a thrown baseball).

Displacement, Velocity and Speed

• Displacement is the difference between an object's starting and ending points.
• Displacement's SI unit is the meter.
• Velocity, acceleration, and displacement are vectors.
• Speed is calculated from distance and time.
• Velocity combines speed and direction.

Graphs and Motion

• Steeper slopes on distance-time graphs mean faster speeds.
• Velocity equals speed in linear motion.
• The moon orbits Earth at a constant speed with changing direction.
• Distance vs. time graphs display object speed.
• Flat lines on a distance/time graph indicate no movement (stationary).

Energy and Motion

• Heat transfers from hot to cold objects.
• Convection occurs when warm air rises and cool air sinks.
• Radiation is heat transfer without a medium.
• Conduction involves heat transfer through direct contact.
• Particles speed up when heated and slow down when cooled.
• Heat causes particles to move farther apart.
• Rubbing hands together creates friction, converting mechanical energy into thermal energy.
• A car engine transforms chemical energy from fuel into thermal energy, which then transforms to mechanical energy.
• Temperature increases due to increased particle motion.