# Glencoe 9th PS Chapter 3 – Forces

Question | Answer |
---|---|

Newton's second law of motion | the net force acting on an object causes the object to accelerate in the direction of the net force |

Acceleration of an object | is determined by the size of the net force & the mass of the object |

acceleration = net force/mass | a = F/m |

unit of acceleration | meters per second squared or (m/s?) |

unit of mass | kilogram |

second law of motion – force | kg X m/s? – also called the newton (N) |

Newton | kg X m/s? |

Friction | force that opposes motion between two surfaces that are touching each other |

Zero acceleration | when something doesn't move |

Static friction | friction between two surfaces that are NOT moving past each other |

Sliding friction | the force that opposes the motion of two surfaces sliding past each other |

Rolling friction | friction between a rolling object and the surface it rolls on |

Air resistance | the force that acts on objects falling through the air |

Gravity | the force that pulls objects toward Earth |

Terminal velocity | the highest velocity (speed) that a falling object will reach |

Law of gravitation | any two masses exert an attractive force on each other- the amount depends on the mass of each & distance apart |

Four basic forces | gravity, electromagnetic, strong nuclear, weak nuclear |

Gravitational acceleration of Earth | F = m X 9.8 m/s?Net force or "F" = mass "m" multiplied by 9.8 m/s? (meters per second squared) |

What direction is the force of Earth's gravity? | It is always downward |

Weight | is the gravitational force exerted on an object – or – "W" |

Weight | W = m X 9.8 m/s?Weight or "W" = mass "m" multiplied by 9.8 m/s? (meters per second squared) |

Free fall | the point at which an object falling to Earth is only influenced by gravity |

Why do projectiles follow a curved path? | because they have horizontal AND vertical velocities |

Centripetal acceleration | is acceleration toward the center of a curved or circular path |

Centripetal force | a force directed toward the center of the circle for an object moving in a circular motion |

Newton's third law of motion | for every action/force on an object there is an equal and opposite reaction force |

The location of what planet was predicted correctly using Newton's laws? | Neptune |

Momentum | the product of an object's mass and velocity |

Momentum | p = m X vproduct or momentum = mass "m" multiplied by velocity "v" |

Newton's second law of motion | F = (mv? – mvi)/tNet force "F" = an object's change in momentum divided by the time "t" over which the change occurs |

Conservation of momentum | a group of objects exerting forces only on each other will equal out – and not lose or gain momentum |