1. 1
6. Motion in two dimensions
Physics
Grade 12
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2. 2
Verticle projectile motion
Projectiles are objects that move through the air.
Objects that move up and down (vertical projectiles) on the earth accelerate with a constant
acceleration g which is approximately equal to 9,8 m·s−2 directed downwards towards the
centre of the earth.
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3. 3
Equations of motion
The equations of motion can be used to solve vertical projectile problems.
v f =v i g t
 v i v f 
 x= t
2
1 2
 x=v i t g t
2
2 2
v f =v i 2g  x
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4. 4
Graphs of motion
Graphs for vertical projectile motion are similar to graphs for motion at constant
acceleration. If upwards is taken as positive the x vs t, v vs t ans a vs t graphs
for an object being thrown upwards look like this:
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5. 5
Conservation of momentum
Momentum is conserved in one and two dimensions
p i =pf
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6. 6
Types of collisions – elastic collisions
An elastic collision is a collision where both momentum and kinetic energy is conserved.
p i =p f
p i1p i2=p f1pf2
KEi =KEf
KE i1KE i2=KEf1KEf2
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7. 7
Types of collisions –
inelastic collisions
An inelastic collision is where
momentum is conserved but
kinetic energy is not conserved.
p i =p f
KE i ≠KEf
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8. 8
Frames of reference and relative velocity
The frame of reference is the point of view from which a system is observed
The velocity of an object is frame dependent. More specifically, the perceived velocity
of an object depends on the velocity of the observer. For example, a person standing on
shore would observe the velocity of a boat to be different than a passenger on the boat.
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9. 9
For more practice or to ask an expert for help on this
section see:
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ESCCW
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