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# Chapter 12 Forces

### Forces

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

Any push or pull on an object | Force |

The net force exerted on an object will produce a proportional acceleration. That is, if a force acts on something, it accelerates. | Newton’s 2nd Law of Motion. |

What explains the relationships among mass, force and acceleration? | Newton’s 2nd Law of Motion – F(force) = m (mass) • a (acceleration) |

The force that opposes motion between two surfaces in contact with (sometimes rubbing against) each other | Friction |

Type of friction between 2 surfaces that are NOT moving past each other | Static Friction – Static means stationary, not moving |

Type of friction between 2 surfaces that are sliding past each other | Sliding Friction – example: When a car skids, its locked wheels slide over the road surface. |

Type of friction between the wheels of a car in motion and the road | Rolling Friction – In this example, the wheels of the car are moving, or rolling. |

The force exerted by air on a moving object | Fluid Friction - also called air resistance and drag |

The largest velocity reached by a falling object when the force of air resistance equals the force of gravity | Terminal velocity |

The force every object in the universe exerts on every other object | Gravity |

The pull of gravity on an object is its __________. | Weight |

The amount of matter in an object is its _______. | Mass |

Mass is also a measure of the _______, or resistance to change in motion of an object. | inertia |

The SI unit for mass is | g or kg |

The SI unit for weight is | N - newtons |

The Si unit for acceleration is usually | m/s2 |

The SI unit for velocity | m/s or km/h |

Is force a vector or scalar quantity | vector - it needs direction |

What law can be stated as “to every action, there is an equal and opposite reaction”? | Newton’s 3rd Law of motion |

The property of a moving object resulting from its mass and velocity | Momentum (p= m • v) |

In the formula p= m • v, what does the p stand for? | Momentum |

What is the SI unit for momentum | kgm/s |

The Newton, the SI unit for force can also be written as the units for m x a combined. What is that? | kgm/s2 |

What force keeps moons in orbit around the planets, the the planets in orbit around the sun? | Gravity |

In the absence of air, how would objects dropped from the same height fall? | At the same rate |

If objects of different masses are dropped from the same height (no air resistance), which will hit the ground first? | They will hit at the same time. |

If a ball and a feather are dropped through the air at the same time, what causes the feather to fall more slowly? | air resistance |

What is the size of the force of the acceleration of gravity on earth (g)? | 9.8 m/s2 towards the center of the earth |

How do we measure Mass in Science? | We measure mass in kg, using a balance. |

How do we measure Weight in Science? | We measure weight in Newtons, using a spring scale. |

Which one does not change and cannot be zero, mass or weight? | mass |

Because you are getting further from the center of the earth, as you climb up a mountain, or ascend in a plane, your weight will _____ | decrease |

What would cause the momentum of a massive object to be 0 N? | If the object was not moving, its velocity would be 0 m/s2. Since p= m • v, any mass with a velocity of 0 m/s2 would have a momentum of 0 N. |

Use Newtons third law to explain how a rocket moves. | The rocket pushes hot gases backwards and the hot gases push the rocket forward. |

Use Newton's third law of motion to explain how a person runs. | A person's foot pushes the ground backwards and down, and the ground pushes the foot, and the attached person, forwards and up. |

What is a free body diagram? | A picture of one object showing all the forces acting on that object as vector arrows. |

If two forces are acting in the same direction, how do you find the net force? | You add the two |

If two forces are acting in opposite directions on the same object, how do you find the net force? | You subtract them |

What if the forces on an object are acting at right angles to each other, how do you find the net force? | You must use pathagorean theorum: a squared + b squared = c squared. |

What devise do we use to measure forces | spring scale |

Define net force | The sum of all the forces acting on an object |

What are some discoveries of Sir Issac Newton | laws of motion, universal gravitation, calculus, lenses and diffraction of light |

Who discovered things fall at the same rate with his experiments rolling balls down a ramp and dropping them off the tower of Piza? | Galileo |

Define inertia | An objects resistance to change in motion |

Why should you wear your seat belt? | Because of inertia, if not you will go flying forward in a head on crash as the car stops. |

Problem solving: What is the force required to move a 5,000 kg car with an acceleration of 4 m/s2? | F = m x a! 20,000 kgm/s2 or 20,000 N |

What is the acceleration of a 4,000 kg car pushed with a force of 12,000 N? | F = m x a! Solve for a. 3 m/s2 |

What is the weight of a 4,000 kg car? | Remember W = m x g. 39,200 N or 39,200 kgm/s2 |

What is the momentum of a 110-kg professional fullback running across the line at 9.2 m/s. | p = m x v. p is momentum and v is speed or velocity. 1012 kgm/s |

What are the 4 universal forces in nature | electromagnetic, strong and weak nuclear, and gravity |

Draw a free body diagram for a jet flying in the air | It should have thrust pointing forward, gravity down, drag backwards, and lift upwards |

Draw a free body diagram for a jet parked on the ground | It should have gravity pointing down and the ground pointing up |

What is the net force on a box with two people pushing on the same side with 5 N of force each to the east. | 10 N east (add them) |

What is the net force on a box if one person pushes with 5 N east and the other pushed 10 N west | 5 N west (subtract them) |

What if one person is rowing a boat with 10 N of force east and the river is pushing the boat with 5 N of force south? | Use Pythagorean theorem. 5 squared + 10 squared = c squared. 11.18 |

Created by:
tbrandt