Vocabulary
The _________ force is always _____________ to the surface. On a horizontal surface, it balances the ________ of the object.
normal, weight
Two objects attract each other with a gravitational force equal to 20N. If the mass of one of the objects is halved while the distance doubles, what is the new force of gravity between the two objects?
from mass: 1/2
from distance: 2=>1/2=>1/22=>1/4
total: 1/2*1/4=1/8
new force=1/8F=1/8*20N=5/2N or 2.5 N
Draw a picture of a person pushing a box to the right along a flat, horizontal surface, and draw arrows to represent the applied force and frictional force.
Applied force=arrow to right in direction of motion
friction=arrow to left to oppose motion
Order the following SI prefixes from largest to smallest: mega, deca, deci, tera, pico, nano, milli
tera, mega, deca, deci, milli, nano, pico
position vs time: flat, horizontal line anywhere on the graph
velocity vs time: flat, horizontal line on the x-axis
What is the attractive force between any two objects with mass?
Force of gravity
A 22 kg rock slides across a floor with a coefficient of friction of 0.62. What is the frictional force acting on the rock? Round your answer to the nearest tenth.
Fn=-(22kg)(-9.8m/s2)=+215.6N
Ff=(0.62)(215.6N)=133.7N
Draw a diagram of a skateboard moving down a ramp. Draw arrows to show the normal force and the force of gravity acting on the skateboard.
Normal force=perpendicular to the angle of ramp
force of gravity=down
Convert 4.6 ns to Ms
1ns=10-9s
1Ms=106s
=4.6*10-15Ms
A student is running at 5 m/s. If she accelerates at 0.5 m/s2, what is her final (instantaneous) velocity after 10s?
vf=5m/s+0.5m/s2*10s
=5m/s+5m/s
=10 m/s
What is the force transmitted through a stretched string, rope, cable, or similar object?
Tension
A 3 kg object is pushed across the floor such that the frictional force is 15 N. What is the coefficient of friction between the object and ground?
coefficient of friction=Ff/Fn
Fn=-mg=-(3kg)(-9.8m/s2)=+29.4N
coefficient of friction=Ff/Fn=15N/29.4N=0.5
-(10kg)(-9.8m/s2)=98N
For each example, label it as a variable, constant, unit, or physical quantity:
a) 5 meters: __________________________
b) Time during an experiment: ___________________________
c) Speed of light (does not change): __________________________
d) Kilogram: __________________________
a) physical quantity
b) variable
c) constant
d) unit
If a student walks 10 meters north, 20 meters south, then 40 meters north, what is their distance, and what is their displacement?
distance=10m+20m+40m=70m
displacement=+10m-20m+40m=+30m=30m North
A force that opposes the relative motion or attempted motion between two surfaces in contact
Friction
Two objects attract each other with a gravitational force equal to 10N. If the mass of both objects is doubled and the distance is tripled, what is the new force of gravity between the two objects?
from mass: 2*2=4
from distance:3=>1/3=>1/32=>1/9
total force change factor:4*1/9=4/9
new force=4/9F=4/9*10N=40/9N or 4.44N
Calculate the gravitational field strength (acceleration due to gravity) on a planet where a 5 kg object experiences a force due to gravity equal to -25N.
g=-25N/5kg=-5m/s2
Convert 1.2 Gm to dm.
1Gm=109m
1dm=10-1m
=1.2*1010
If you run at a speed of 2 m/s for 2 minutes, how far did you travel?
2min=120s
distance=2m/s*120s=240m
An interaction (push or pull) that can cause an object to change its motion; measured in newtons (N).
Force
What is the mass of an object if the force of gravity acting on it is equal to -196N?
-196N/-9.8m/s2
=20kg
What is the force of gravity acting on an 8 kg object on Venus where acceleration due to gravity is equal to -8.87 m/s2?
(8kg)(-8.87m/s2)
=-70.96N
A student is testing how sunlight affects plant growth for three different plants. They give all plants the same amount of water, the same soil, and the same size pot. The plants get 12 hours, 6 hours, and 2 hours of sunlight respectively. What is one variable and constant in this experiement?
variable=amount or time of sunlight
constant=water, soil, and pot size
A bike goes from 10 m/s to 2 m/s in 6 s. What is its acceleration?
a=(2m/s-14m/s)/6s
=-12m/s/6s
=-2m/s2