SMA_1-_Types_of_forces

Forces in Action

  • Understanding the science behind movement.

What is Force?

  • Definition: A physical concept describing the interaction between two objects that can change their motion.

  • Simplified: A push or pull that causes an object to move, stop, or change direction.

Types of Forces

Contact Force

  • Definition: Forces acting between two objects in physical contact.

Non-Contact Force

  • Definition: Forces that act without physical contact between objects.

Types of Forces

  • Contact Forces:

    • Friction

    • Tension

    • Applied Force

    • Normal Force

  • Non-Contact Forces:

    • Gravity

    • Magnetic Force

    • Electrostatic Force

Contact Forces

Friction

  • Definition: A force occurring when two surfaces rub against each other, causing resistance to motion.

  • Example: Pushing a heavy box versus a lighter box.

Characteristics of Friction

  1. Opposes relative motion or attempted motion.

  2. Magnitude depends on surface nature and normal force.

  3. Coefficient of Friction indicates how sticky or slippery surfaces are.

Applications of Friction

  1. Provides grip for walking and driving.

  2. Generates mechanical resistance.

  3. Prevents motion on inclined planes.

Types of Friction

  1. Static Friction:

    • Acts when an object is stationary relative to the surface, preventing movement.

  2. Kinetic Friction:

    • Acts when an object slides over a surface, typically less than static friction.

  3. Rolling Friction:

    • Acts on rolling objects (e.g., wheels), much weaker than static or kinetic friction.

Resistance

  • Definition: A force that slows down or stops another object's motion.

  • Example: Air resistance acting on a paraglider.

Characteristics of Resistance

  1. Acts opposite to the direction of motion.

  2. Depends on speed, shape, surface area, and medium.

  3. Converts kinetic energy into thermal energy.

Types of Resistance

  1. Frictional Force

  2. Air Resistance (Drag)

  3. Viscous Force

  4. Normal Resistance

Tension Force

  • Definition: Created when an object is pulled in opposite directions.

  • Example: Tension in ropes of a swing.

Characteristics of Tension

  • Direction acts along the rope, pulling away from the object.

  • Magnitude remains constant under ideal conditions but changes with mass or friction.

Applications of Tension

  1. Supporting loads.

  2. Transmitting force in pulleys.

  3. Stability in suspended structures.

Formula for Tension

  • Horizontal Pull: T = m.a

  • Vertical Hanging Object: T = m.g

  • Inclined Plane: T = m.g.sin(θ)

Applied Force

  • Definition: One object pushes or pulls another.

  • Example: Kicking a soccer ball.

Characteristics of Applied Force

  • Direction determines the object’s motion.

  • Magnitude can vary; unbalanced forces lead to motion.

Normal Force

  • Definition: The push exerted by a surface on an object.

  • Example: A player's foot pushing against a soccer ball.

Characteristics of Normal Force

  • Acts perpendicular to the surface.

  • Magnitude equals the perpendicular component of all forces pressing the object against the surface.

Formulas for Normal Force

  • On a horizontal surface: N = m.g

  • On an inclined plane: Adjust according to angle.

  • Under applied forces: N = m.g ± F_app sin(θ)

Non-Contact Forces

Gravity

  • Definition: A force pulling objects toward each other.

  • Example: Jumping on a trampoline and falling back.

Characteristics of Gravitational Force

  • Exists between any two masses; always attractive.

  • Acts along the line joining the centers of masses.

Formula for Gravitational Force

  • F₁ = G.(m1.m2) / p²

  • On Earth's surface: Fg = m.g

Magnetic Force

  • Definition: A non-contact force between magnets.

  • Example: A crane using magnets to pick up metal objects.

Electrostatic Force

  • Definition: Force between electrically charged objects.

  • Example: Lightning caused by electrical charge buildup.

Balanced and Unbalanced Forces

Balanced Forces

  • Definition: Forces cancel each other out, resulting in no net force.

  • Example: A skydiver reaching terminal velocity where air resistance balances weight.

Characteristics of Balanced Forces

  • Object remains stationary or continues moving at constant speed.

Unbalanced Forces

  • Definition: Forces do not cancel, resulting in acceleration.

  • Example: Kicking a ball causing it to move.

Characteristics of Unbalanced Forces

  • Always cause a change in motion.

  • Net force is greater than 0.

Combining Forces

Net Force

  • Overall force acting on an object.

  • Forces in same direction: Add them.

  • Forces in opposite directions: Subtract smaller from larger.

Combining Forces at Right Angles

  • Use the Pythagorean Theorem to calculate net force when forces are applied at right angles.

Friction in Stopping Forces

  • Friction aids in situations like braking and providing grip.

  • Static friction stops a block from moving, while dynamic friction is less and heats materials.

Stopping Distance

  • Defined as the distance a car travels to stop, calculated as:

    • Stopping distance = Thinking distance + Braking distance.

Thinking Distance

  • Distance traveled while reacting to a danger.

Braking Distance

  • Distance traveled during the actual braking process.

Review Test Questions

  1. Define force.

  2. Identify types of forces illustrated in images.

  3. Describe the function of friction.

  4. What is the role of normal force?

  5. Explain gravity and give examples.