Part 3: Newton’s Law of Motion

Part 3: Newton’s Law of Motion

WONG Enoch

_{1st Law: The Law of Inertia}

• Every object at rest, or moving in a constant velocity in a straight line, will continue in that state unless it is compelled to change by an external force exerted upon it.

• Example: Before the penalty kick of football player, the ball is at rest; to perform a kick, the football player has to apply a force (kicking) to a football to overcome it’s inertia. This makes the football moves forward.

Can you give some more examples about inertia in sports?

Cycling

Taking cycling as an example, how does the Newton’s First Law of Motion affect their performance?

Swimming

• Taking swimming as an example, how does the Newton’s First Law of Motion affect their performance?

• An athlete needs to pull his arm and legs to produce force to move his body forward. After one pull, the body will keep moving forward due to the Newton’s 1st law of motion.

   

  A good swimmer will possess good stroke skills so that he will produce less water resistance(other force). He will also keep a good balance between stroke and straight his body to slide in the water so as to make use of the inertia to move forward.

Multiple Choice

Which of Newton's Laws is demonstrated by a ball rolling to a wall then stopping?

• A. Newton's first law

• B. Newton's second law

• C. Newton's third law

• D. Newton's law of acceleration

Multiple Choice

According to Newton's first law of motion......

• A. An object in motion will slow down when moving down a hill

• B. An object in motion will stay in motion unless acted upon by an outside force

• C. An object in motion will always move sideways when acted upon by an outside force

• D. An object in motion will stay in motion when it is acted upon by an outside force

Multiple Choice

Why do you lean towards the left when a car turns right ?

• A. Because of gravity

• B. Because of reaction force

• C. Because of velocity

• D. Because of inertia

Multiple Choice

"An object in motion (or at rest) will to stay in motion (or at rest) until an outside force acts upon it."

• A. Newton's First law

• B. Newton's Second law

• C. Newton's Third Law

• D. Newton's Fourth Law

Multiple Choice

The tendency of an object to resist changes in its motion is...

• A. inertia

• B. force

• C. acceleration

• D. velocity

2^nd Law: The Law of Acceleration

• The acceleration of an object is proportional to the force causing it and inversely proportional to the mass of the object; the acceleration takes place in the direction in which that force acts. 

• Example: In a volleyball match, a more powerful spiking causes a greater acceleration of the ball making it more difficult for the defenders to receive the spike.

F = ma

Force = Mass of the object x Acceleration.

In order to generate a greater acceleration, a stronger force must be exerted. If the mass of the object and the acceleration are known, the force required to give that acceleration can be calculated 

In what aspect do we apply F = ma in sports?

Multiple Choice

Force = Mass x Acceleration

• A. Newton's First law

• B. Newton's Second law

• C. Newton's Third Law

• D. Newton's Fourth Law

Multiple Choice

Which of the Newton's Laws describes the amount of force applied to accelerate an object's mass?

• A. Newton's First law

• B. Newton's Second law

• C. Newton's Third Law

• D. Newton's Fourth Law

Multiple Choice

If you kick a bowling ball and a tennis ball with the same amount of force, according to Newton's 2nd Law what will happen?

• A. The tennis ball will travel faster than the bowling ball

• B. The bowling ball will travel faster than the tennis ball

• C. The bowling ball will travel faster, but cover a shorter distance

• D. Both the balls will travel the same distance

Multiple Choice

According to Newton’s second law of motion, force is equal to mass times ______________________.

• A. inertia

• B. weight

• C. acceleration

• D. direction

3^rd Law: The Action / Reaction Law

• When an object exerts a force on a second object, there is a force equal in magnitude but opposite in direction exerted by the second object on the first.

• A high jumper exerts a force on the ground when taking-off. The ground reaction force in upward direction is generated acting upon the jumper to propel him / her over the bar.

In what situation do we apply the law of action and reaction in sports?

Multiple Choice

"For every action, there is an equal and opposite reaction."

• A. Newton's First law

• B. Newton's Second law

• C. Newton's Third Law

• D. Newton's Fourth Law

Multiple Choice

If the action force is of 5 N, then the reaction force will be .....

• A. 5 N in the same direction

• B. 5 N in the opposite direction

• C. 10 N in the same direction

• D. 10 N in the opposite direction

Multiple Choice

A Newton is a unit of...

• A. force

• B. inertia

• C. acceleration

• D. velocity