Forces and Newton’s LawsQuiz Self-Testing Guide 2017

~Due day of the quiz~ANSWERS IN BOLD

Students should be able to . . .
Forces
  1. Draw all the force arrows for the forces acting on a boy pulling a wagon.
  2. What do you call a force that moves something in a circle?
NOT TESTED ON THIS QUIZ
A centripetal force will keep something moving in a circle.
  1. Put the list of objects in order from least inertia to greatest inertia: cell phone, milk cow, pencil, student, textbook.
Inertia is an object’s resistance to a change in motion; like how easy or difficult it is to get an object at rest to move. In order of least to greatest: pencil, cell phone, textbook, student, milk cow.
  1. Which has more inertia a penny or a quarter? How could you do a test to prove it?
A quarter has more inertia than a penny because it has a higher mass. You can test this by sliding a penny at a quarter, and then sliding a quarter toward a penny. Whichever coin moves the farthest after being hit has the LOWEST inertia.
  1. Describe Newton’s 1st Law of motion
You can describe Newton’s first Law without defining it by explaining that an unbalanced force is required to either create or change motion.
  1. When you kick a soccer ball, is that an example of balanced or unbalanced forces on the ball.
If the soccer ball moves when you kick it, the force you added has to be unbalanced because motion was created. The balanced forces on the ball kept it still until you added
  1. Use Newton’s 1st Law to describe why Kimberly suddenly shifts to the right when riding in a car that suddenly turns left.
Newton’s 1st Law states that Kimberly wants to keep moving in the same direction (stay in motion). So when the car changes direction, Kimberly tries to keep going straight, this makes her appear to move to the right as the car moves left.
  1. Can Newton’s 1st Law be described by a formula?
No. There is no formula for Newton’s 1st Law or for inertia. We just know that inertia increases as mass increases.
  1. If Andrea is riding a bike at a steady pace, is there an unbalanced force acting?
For an unbalanced force to be acting there would need to be a change in motion. If the bike is going at a steady speed, then there are no unbalanced forces.
  1. What is the formula for Newton’s 2nd Law?
F = ma where F = force, m = mass, and a = acceleration.

  1. Draw the force square.
  1. What formula would you use to find acceleration if you know the mass and force? What formula would you use to find mass if you know the acceleration and force applied?
Based on the “force square”,to find acceleration usea = F/m. To find mass usem = F/a.
  1. If the force is constant,will a 10 kg or a 5 kg object have the greatest acceleration? How do you know?
For a set force, the high mass object (10kg) will have less acceleration because it takes more force to move a larger mass.
  1. What direction will the friction force point for a hockey puck on ice? How do you know?
The object will move to the right because the object always accelerates in the same direction as the force that was applied
  1. What force would be required to accelerate a 10 kg cart at 2 m/sec2? SHOW YOU WORK!
F = ma F = (10 kg)x(2 m/sec2)
F = 20kg * m/sec2 - A Newtonis a kg * m/sec2
F = 20 Newtons
  1. If a 100 g ball is accelerating down the hill at 5 m/sec2, what is the size of the force causing the acceleration? SHOW YOU WORK!
F = ma F = (100 g)x(5 m/sec2)
F = 500 g m/sec2 - but for Newtons we need kg m/sec2
F = 0.500Newtons (Note that we didn’t start with kg which are the standard for a Newton)
  1. Kiahra pushed a 5 kg box of dance flyers with a force of 10 N. What is the acceleration of the box? SHOW YOU WORK!

So a = F/m
a = 10 N/ 5 kg
a = 2 m/sec 2
  1. What mass can Kevin accelerate to 5 m/sec 2using a 10 N force? SHOW YOU WORK!

So m= F/a
m= 10 N/ 5 m/sec 2
m= 2 kg
  1. Describe Newton’s 3rd Law.
For every action force, there is an equal and opposite reaction force is Newton’s 3rd Law
  1. Describe the action and reaction FORCES when you kick a ball.
When you kick a ball, your foot puts an action force on the ball, and the ball put a reaction force onto your foot.
  1. What is the difference between action/reaction forces and balanced/unbalanced forces acting on an object?
Action/reaction force pairs act on DIFFERENT objects. Balanced/unbalanced forces focus on the forces acting on a single object. Balanced/unbalanced forces determine if the object will be in motion.
  1. If I apply a push force to one of the moveable demo tables, what is the size and direction of the force it applies to my hand?
When I apply a force on the moveable demo table, the table exerts a force on my hand that is equal in size, but opposite in direction.
  1. Can a reaction force ever be greater or less than an applied force?
NO. Newton’s 3rd Law says the reaction force must be equal in size, and opposite in direction compared to the action force.
  1. What’s the relationship between mass and weight?

Weight is the force of gravity pulling on the object. Mass is the amount of matter of the object.

  1. Define how each of Newton’s Laws applies to Marissa kicking a soccer ball or a car moving away from a stop light.

According to Newton’s 1st Law, the soccer ball will move if Marissa applies an unbalanced force. According to Newton’s 2nd Law a soccer ball will accelerate more than a basketball because the soccer ball has less mass. According to Newton’s 3rd Law, when Marissa applies a force to the soccer ball with her shoe, the ball also applies an equal and opposite reaction force to her shoe!

According to Newton’s 1st Law, the force that a car motor applies to move it away from a stop light must be large enough to unbalance all the other forces around. According to Newton’s 2nd Law, the acceleration created will increase with the size of the force and decrease as the mass of the carincreases. The force that the motor puts on the axel to move the car is equal and opposite to the force that the axel puts back on the motor.