PHYSICS & ENERGY UNIT

Question 1

Force

Answer 1

= push or pull; described by

strength (N) and direction

Unit of Force = Newton (N); where 1N = 100 g

Force Instrument: force meter/spring scale (N)

Force is represented as an arrow (with direction)

longer arrow ~ greater force

Question 2

Net Force

Answer 2

= combining forces

if forces are in the same direction, you

add together to produce a net force.

if forces are in opposite directions, you
subtract to produce a net force in the
direction of the larger force.

if opposing forces are of equal strength,

there is no (zero) net force.

Question 3

Unbalanced Forces

Answer 3

Unbalanced forces occurs when a net force is
present causing a change in the object’s
motion.

if two unbalanced forces are in the same
direction, the net force is the sum (+) of the
forces.

if two unbalanced forces are in the opposite
directions, the net force is the difference (-)
between the forces.

Question 4

Balanced Forces

Answer 4

Balanced forces occurs when equal (strength)
forces are acting in opposite directions. The net
force is zero. Balanced forces does not change
the object’s motion.

Question 5

Efficiency

Answer 5

Efficiency of a machine compares the output
work to the input work. Maximum efficiency is
100% but all machines have an efficiency of
less than 100% because some work is wasted
due to friction (heat loss). To calculate
efficiency the following formula is used:

Question 6

Friction:

Answer 6

the force that two surfaces exert
on each other when they rub against each
other.

Question 7

Factors Affecting Friction:

Answer 7

1) weight

2) rough versus smooth surfaces

3) lubricants (oils, grease); ball bearings

4) surface area

Question 8

Friction:

Answer 8

a force that acts in a direction opposite to
the direction of the object’s motion. Four (4) types:

Question 9

Static Friction:

Answer 9

friction that acts on objects that
are not moving. Static greater than sliding, rolling,
fluid friction.

Question 10

Sliding Friction:

Answer 10

friction when two surfaces slide
over each other.

Question 11

Rolling Friction:

Answer 11

friction when an object rolls
across a surface. To reduce friction, use wheels or
ball bearings.

Question 12

Fluid Friction:

Answer 12

Friction when an object moves
through a fluid. To reduce friction, use oils &
lubricants; streamline.

Question 13

Gravity:

Answer 13

is an attractive force between
objects containing mass.

Question 14

Factors Affecting Gravity:

Answer 14

Mass - amount of matter (atoms) in an object

Distance - length between two points

increase mass ~ increase gravity

increase distance ~ decrease gravity

Question 15

Terminal Velocity:

Answer 15

maximum velocity of a
free falling object occurs when the force of air
resistance equals the weight of the object.
Terminal velocity represents balanced forces
where upward air resistance equals downward
gravity.

Question 16

Mass:

Answer 16

the amount of matter (atoms) in an object.

Question 17

Free Fall:

Answer 17

only gravity acting on a falling object. Objects
accelerate as they free fall because gravity is an unbalanced
force. In a vacuum, all objects in free fall accelerate at the
same rate regardless of their masses. Gravitational
acceleration near Earth is 9.8 m/s2.

Question 17

Weight:

Answer 17

the gravitational force exerted on an
object’s mass.

Question 18

Air Resistance:

Answer 18

is a type of fluid friction as an object
falls through the air. Greater surface area of object ~
increase in air resistance ~ slower the object falls. Air
resistance increases as velocity increases.

Question 19

Projectile Motion:

Answer 19

Projectile: an object that is thrown. A projectile
(with horizontal motion) will fall at the same rate as
any dropped object.

Question 20

Centripetal force:

Answer 20

a force of attraction that
occurs when an object moves in circular
motion.

Question 20

Projectile:

Answer 20

an object in motion along a path.

Question 21

Trajectory:

Answer 21

the path a projectile takes while in
motion under the influence of forces.

3. 9.8 meters/ second2

Question 22

Terminal velocity:

Answer 22

maximum speed a free
falling object reaches when the force of gravity
on the object equals the upward force of air
resistance.

98 meters/sec

Stops (goes to

Question 22

Newton’s 1st Law of Motion Inertia:

Answer 22

an
object at rest will remain at rest and an
object moving at a constant velocity will
continue moving at a constant velocity,
unless it is acted upon by an unbalanced
force. Gravity and friction are unbalanced
forces.

Question 23

Inertia:

Answer 23

is the tendency of an object to resist a
change in motion.

Question 23

Newton’s 2nd Law of Motion:

Answer 23

acceleration
depends on the object’s mass and the force
acting on the object. So:

Force (N)= Mass (kg) x Acceleration (m/s2)

F=MA and A=F
1N = 1kg·m/s

M

Question 24

Inertia:

Answer 24

objects do not want to change
their motion (“lazy”); objects at rest want
to remain at rest, objects in motion want
to remain in motion unless acted upon by
an unbalanced force.

2. Because spaceship is not in contact with
   anything and there is no unbalanced
   force acting on it
3. gravity