Chap 4: Dynamics II - Forces

Question 1

What is Newton’s first law of motion?

Answer 1

every object will continue in its state of rest or uniform motion in a straight line unless a resultant force acts on it

Question 2

Another name for Newton’s first law?

Answer 2

law of inertia

Question 3

What is a balanced force?

Answer 3

When all the forces acting on an object is balanced and the resultant force is zero

Question 4

What happens to an object when its resultant force is zero? (balanced force)

Answer 4

object can be…
- at rest
- or in constant velocity
the acceleration is ZERO

Question 5

Define inertia

Answer 5

reluctance of an object to change its state of rest or motion due to mass

Question 6

Does mass affect inertia?

Answer 6

Yes
The greater the mass, the more inertia

Question 7

What is Newton’s Second Law of Motion?

Answer 7

when a resultant force acts on an object of constant mass, object will accelerate in direction of resultant force

Question 8

When are forced unbalanced?

Answer 8

when the resultant force is NOT zero, so there will be acceleration

Question 9

How to calculate resultant force?

Answer 9

product of mass and acceleration

F=ma

Question 10

What are the effects on a resultant force?

Answer 10

causes objects to:
- move
- stop
- change velocity

Question 11

Effects on Newton’s second law of motion?

Answer 11

objects can be accelerating or decelerating

Question 12

What is Newton’s third law of motion?

Answer 12

for every action, there’s an equal and opposite reaction

Question 13

four key points of newton’s third law

Answer 13

1. forces occur in pairs (action & reaction)
2. action and reaction are equal in magnitude
3. action and reaction act in opposite directions
4. action and reaction act on different bodies

Question 14

2 main points to consider when drawing free body diagrams

Answer 14

• include ONLY object of interest
• and all external forces acting ON the object itself

Question 15

How to find resultant force?

Answer 15

vector addition or drawing vector diagram

Question 16

What happens when 3 forces balance each other? (equilibrium)

Answer 16

• resultant force is zero
• forms a closed triangle

Question 17

Define friction

Answer 17

a contact force that opposes or tends to oppose motion between surfaces in contact

Question 18

Examples of positive effects of friction?

Answer 18

• walk without slipping with friction
• objects can slow down if needed with friction

Question 19

Examples of negative effects of friction?

Answer 19

• cars are less efficient
• causes wear and tear

Question 20

How to reduce negative effects of friction?

Answer 20

use:
- wheels
- ball bearings
- lubricants and polished surfaces
- air cushion

Question 21

How to enhance positive effects of friction?

Answer 21

use:
- treads
- parachutes
- chalk

Question 22

What happens when objects fall without air resistance? [gravity only]

Answer 22

• objects experience free fall
• constant acceleration of 10m/s^2
• free fall on dependant on mass or size

Question 23

What happens to objects that falls with air resistance?

Answer 23

object falls with decreasing acceleration

Question 24

How to reduce air resistance?

Answer 24

have a streamlined shape

Question 25

Define terminal velocity

Answer 25

when air resistance equals weight
- object travels at constant speed
- zero acceleration, constant velocity

Question 26

What does air resistance do?

Answer 26

• opposes motion of object
• increases with speed of object
• increases with size/surface area of object
• increases with density of air