Study Guide: Chapter 9- Measuring Motion

  1. How do you know you are moving?

motion: an object is in motion if its distance from another object is changing.

reference point: a place or object used for comparison to determine if something is in motion.

a. For example, imagine you are on a train sitting in a seat next to your best friend. The train is going 70 mph. If you use your friend as the reference point, it would appear that you are not moving. BUT if you use the tree outside as a reference point it would appear that you are moving 70 mph.
2. What is speed?

  1. If you know the distance an object travels in a certain amount of time, you can calculate the speed of the object. BECAUSE…the speed of an object is the distance the object travels per unit of time.
  2. The speed of most objects is not constant, and therefore, the average speed is often used in place of the instantaneous speed (the actual speed at that instant – like the speed measurements that police officers make with “radar guns”).
    Average speed = final distance – initial distance

Time

What is velocity? The direction and speed an object travels.

4. What is acceleration?

The rate at which velocity changes by way of increasing speed, decreasing speed, or changing direction.

5. How can we know if an object is accelerating?

Acceleration = Final speed – Initial speed
Time

Chapter 10 - Force

  1. What is force? A push or pull

2) /
  1. What is the difference between a balanced and an unbalanced force?
Balanced forces – object does not move
Unbalanced forces change the velocity of an object and cause an object at rest to move.
Forces Acting in Same Direction
5N + 10N Net Force: 15 N (unbalanced)

Forces Acting in Opposite Directions
5N + 10N Net Force: 5 N (unbalanced)

5N 5N Net Force: 0 N (balanced)

  1. Describe two examples of force.
Gravity and Friction
  • Friction is a contact force.
  • The law of universal gravitation states that all objects are attracted to each other by gravity.
  • Friction can stop or slow down objects sliding past each other.
  • Friction acts in the opposite motion of the object.
  • There are 4 different kinds of friction.
  • Terminal velocity and free fall

  1. Is friction useful or not?

Helps us walk and stop our car

  1. What is the difference between mass and weight?

Mass is the amount of matter and weight is the measure of gravitational force

  1. What factors affect gravity and friction?

Friction depends on type of surface.

Gravity depends on distance and mass.

  1. What are Newton’s Laws of Motion?

Newton's First Law

  • An object's motion can only be changed by unbalanced forces.
  • According to Newton's 1st Law, the motion of an object is not changed by balanced forces acting on it.
  • Inertia is the tendency of an object to resist its change in motion

Newton's Second Law

  • According to Newton's 2nd Law, an objects acceleration is the net force on the object divided by its mass.
  • In circular motion, a centripetal force pulls an object toward the center of the curve.
  • Formula Force = mass x acceleration

Newton's Third Law

  • Newton's 3rd Law states that when one object applies a force on another, the second object applied an equal force in the opposite direction on the first object.
  • The forces of a force pair do not cancel because they are acting on different objects.
  • According to the law of conservation of momentum, momentum is conserved during a collision unless an outside force acts on the colliding objects.

Formula Momentum = mass x velocity