Forces
Rule 1: Draw the diagram (make it simple).
Rule 2: The force arrow starts at the centre of the object being acted on.
Rule 3: Always check the units!!!!!!!!!!!!!
Newton’s 3 Laws of Motion
Newton’s 1st Law:
An object will remain in a constant state of motion unless acted upon by a
resultant force.
Newton’s 2nd Law:
The acceleration of an object is directly proportional to the magnitude of the
resultant force acting upon it, and inversely proportional to the object’s own mass.
Newton’s 3rd Law:
If body A exerts a force on body B, then body B will exert a force of the
same size and type, but in the opposite direction, on body A.
Write your own version of each of these laws in simple language, because if you can
explain it simply it shows you really understand it
Newton’s 1st Law means:
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Newton’s 2nd Law means:
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Newton’s 3rd Law means:
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Air Resistance
Weight
Friction
Upthrust
A)
B)
C)
`
D)
D)
E)
F)
Stationary
G)
Faster
Constant Speed
Slower
Stationary
Constant
Speed
Which way will each of these boxes move and why?
(A)
(B)
(C)
Box A will move to the left because ----Box B will move diagonally---Box C will move
diagonally
9 N beats 4N and both 3 N cancel out--up to the left because both—down to the left
because
-9N’s beat the 3N and 4N-----7 and
9 beats 3
Add arrows next to each of these photos showing how the sizes of the friction and forwards
force compare to each other. Draw the arrow representing friction in blue and the arrow
representing the forwards force in red. Are the forces balanced or unbalanced in each case?
Speeding up
Still/stopped
Slowing down
In speeding up the forces are unbalanced with the forward force being greater. In
still/stopped the forces are balanced. In slowing down the forces are unequal with friction
being greater.
20
0
1000
100
0
20000
Why do objects float?
Objects float because the upthrust and gravity are equal
Circle the correct definition of density:
The amount of space an object takes up.
How heavy an object is for its size. Mass per unit Volume
The width and solidity of an object. How wide and hard it is
The weight of an object.
Calculate the densities of blocks A-D. Remember! You must calculate the volume of each block
first:
(A)
(B)
14g
(C)
24g
(D)
16g
A) Volume:
1*1*1=1
Density: 14
B) Volume:
2*2*2=8
Density: 3
C) Volume:
3*3*3=27
Density:0.59
D) Volume:
4*4*4=64
Density:0.54
35g
Newton’s Second Law, as it is stated at the start is talking about
acceleration. It says that if you double the resultant force on the
object you double the acceleration of the object and if you double
the mass of the object you make it twice as hard to push so you
halve its acceleration.
Therefore the equation is
F=M*A
𝒂=
𝑭
𝑚
so
𝑭 =? & 𝑚 =?
M=F/A
Use these equations to answer the following questions.
1
2
3
4
5
6
7
Easy
What is the unit of
force?
Newton
Write the equation
needed to calculate
force if the mass and
acceleration is known.
F=M/A
Rearrange the force
equation to calculate
mass.
M=F/A
Rearrange the force
equation to calculate
acceleration.
A=F/M
What is the force if the
mass is 20 kg and the
acceleration
80 m/s/s?
1600 N
What is the force if the
mass is 50 kg and the
acceleration is 900
m/s/s/?
Medium
What is the force if the
mass is 3.5 kg and the
acceleration is 80 m/s/s?
What is the force if the
mass is 800 kg and the
acceleration is 60 m/s/s?
Hard
What is the force of a ball
with a mass of 5 kg if it
accelerates at 10 m/s/s?
What is the force on a
man if he accelerates at
42 m/s/s and has a mass
of 112 kg?
What is the acceleration
if the mass is 80 kg and
the force
75 N?
What is the mass if the
force is 90 N and the
acceleration is
80 m/s/s?
What is the mass if the
force is 20 N and the
acceleration is 80 m/s/s?
What is the acceleration
of a cat if it has a mass of
8 kg and hits the cat flap
with a force of 65 N?
What is the mass of a dog
if it accelerates at 20
m/s/s and has a force of 8
N?
Draw a car moving forward
on a road. What are the
forces acting upon the
car? Draw arrows to show
them.
What are the forces
acting upon a box being
pushed by a man? Draw
arrows to show the forces.
What is the acceleration
if the force is 50 N and
the mass is 100 kg?
2
What is the acceleration
if the force is 74 N and
the mass is 655 kg?
8.85
What is the force if the
mass is 40 kg and the
acceleration is
23 m/s/s?