### Forces On Bodies Contact And Non Contact Forces

**How to Remember Physics Concepts**

**Contact Forces:**

Force | Key Points |
---|---|

Normal force |
The force exerted by a surface perpendicular to the surface. It prevents objects from sinking into the surface. Remember: “Normal” means “perpendicular”. |

Friction |
The force that opposes the motion of two surfaces in contact. It is caused by the interlocking of microscopic irregularities on the surfaces. Remember: Friction is like a “tug-of-war” between surfaces. |

Tension |
The force exerted by a rope, cable, or other flexible object that is under tension. Remember: Tension is like a “stretching” force. |

Spring force |
The force exerted by a spring when it is stretched or compressed. Remember: Springs are like “bouncy” objects that store energy. |

**Non-contact Forces:**

Force | Key Points |
---|---|

Gravitational force |
The force of attraction between two objects with mass. The greater the mass of the objects, the greater the gravitational force. Remember: Gravity is the force that keeps us on the ground. |

Electrostatic force |
The force of attraction or repulsion between charged particles. Remember: Electrostatic force is like a “magnet” force, but it works with electric charges. |

Magnetic force |
The force exerted by a magnet on a magnetic material. Remember: Magnetic force is like a “super-strong” electrostatic force that only works with magnets. |

**Newton’s Laws:**

Law | Key Points |
---|---|

Newton’s first law of motion (law of inertia) |
An object at rest will remain at rest, and an object in motion will remain in motion at a constant velocity in a straight line unless acted upon by an external force. Remember: Inertia is like “laziness” - objects don’t want to change their motion. |

Newton’s second law of motion (law of acceleration) |
The acceleration of an object is directly proportional to the net force acting on the object and inversely proportional to the mass of the object. Remember: The more force you apply to an object, the faster it will accelerate. The more massive an object, the harder it is to accelerate. Use the formula: (F = ma), where (F) is the net force, (m) is the object’s mass and (a) is its acceleration. |

Newton’s Third law of motion (law of action and reaction) |
For every action, there is an equal and opposite reaction. Remember: Actions always have “reaction partners”. |

**Applications of Newton’s Laws:**

Application | Key Points |
---|---|

Equilibrium of forces |
When the net force acting on an object is zero, the object is in equilibrium. Remember: Equilibrium is like “balancing” forces. |

Dynamics of a particle |
The study of the motion of a particle under the influence of forces. Remember: Particle dynamics is like “tracing” the path of a moving particle. |

Motion under gravity |
The study of the motion of objects under the influence of gravity. Remember: Gravity always “pulls” objects down. |

Projectile motion |
The study of the motion of objects launched into the air at an angle. Remember: Projectile motion is like throwing a “ball”. |

Circular motion |
The study of the motion of objects moving in circles. Remember: Circular motion is like “going round and round”. |

Work and energy |
The study of the relationship between work and energy. Remember: Work is the “transfer of energy” between objects. |

Impulse and momentum |
The study of the relationship between impulse and momentum. Remember: Impulse is the “change in momentum” due to a force applied over a short time. |

**Collisions | The study of the interaction between objects that collide. Remember: Collisions can be “fun” but also cause damage. |