10. Projectile Motion

Question 1

What is projectile motion?

Answer 1

The movement of a body through the air following a curved flight path under the force of gravity.

Question 2

What is a projectile?

Answer 2

A body launched into the air and subjected to weight and air resistance forces.

Question 3

What can the flight path a projectile takes be represented by?

Answer 3

A simple graph of height against horizontal distance travelled

Question 4

What 4 factors is the horizontal distance travelled by a projectile primarily affected by?

Answer 4

• Speed of release
• Angle of release
• Height of release
• Aerodynamic factors (bernoulli and magnus)

Question 5

How does the speed of release affect the horizontal distance travelled by a projectile?

Answer 5

• The distance travelled by the speed of release -> Newton’s second law of acceleration.
• The greater the outgoing speed of the projectile, the further it will travel.
• Therefore, Olympic throwers will train to generate maximum power from the arms, shoulders, legs and chest

Question 6

How does the angle of release affect the horizontal distance travelled by a projectile?

Answer 6

• 90 degrees -> the projectile will accelerate vertically up and come straight back down, travelling 0m
• 45 degrees -> optimum angle to maximise horizontal distance
• > 45 degrees -> the projectile reaches peak height too early and rapidly returns to the ground
• <45 degrees -> the projectile doesn’t reach sufficient height to maximise flight time

Question 7

How does the height of release affect the horizontal distance travelled by a projectile?

Answer 7

• 45 degrees is the optimum angle of release if the release height and landing height are equal, however if the release height is higher or lower than the landing height, the optimal angle will change.
• Release height above landing height -> (positive relative release height) e.g. javelin- the optimal angle is less than 45 degrees as the projectile has an increased flight time due to the increased height of release
• Release height below landing height -> (negative relative release height) - the optimal angle is more than 45 degrees as the projectile needs an increased flight time to overcome the obstacle

Question 8

What is a parabolic flight path?

Answer 8

A flight path symmetrical about its highest point caused by the dominant weight force of a projectile.

Question 9

What is a non-parabolic flight path?

Answer 9

A flight path asymmetrical about its highest point caused by the dominant force of air resistance on a projectile.

Question 10

What is the Bernoulli principle?

Answer 10

• Creation of additional lift force on a projectile in flight resulting from Bernoulli’s conclusion that the higher the velocity of air flow, the lower the surrounding pressure.
• Lift force can be created in flight based on the shape of a projectile.
• The effect means a projectile will hang in the air and extend the horizontal distance covered.
• Curved upper surfaces forces air flow to travel further and therefore faster.
• The flat underneath means air travels a shorter distance and therefore slower.
• As velocity increases, pressure decreases, therefore curved upper surface- low pressure zone is created.
• e.g. discus becomes a projectile launched at an optimal angle of 17 degrees

Question 11

Downward force- the venturi effect example

Answer 11

The downward lift created by formula 1 car design: air flow diagram with high velocity air flow and low pressure underneath the car and spoiler

Question 12

What is the magnus effect?

Answer 12

• The magnus effect works on the same theoretical basis as the Bernoulli effect
• The spin determines the direction, velocity and pressure of air flow around it.
• A pressure gradient is once again formed and a Magnus force is created which deviates the flight path.