Newton's Laws
Physics: AQA A Level, topic 4.1.16
Newton’s 1st Law
Newton's 1st Law says that the velocity of an object will only change if a resultant force is acting on the object. This applies to a stationary (still) or moving object.
Stationary (still)
- If an object is stationary (not moving) and there is no resultant force acting on it, it will stay stationary.
Moving
- If an object is moving and there is no resultant force acting on it, the object will continue moving in the same direction at the same speed.
- This means that the object will continue moving at the same velocity.
- This also means that the velocity of an object will only change if a resultant force is acting on the object.
Newton's 2nd Law
A force may cause a mass to accelerate. This acceleration can be a change in speed, a change in direction or a change in both speed and direction. This is Newton's 2nd Law.
Resultant force
- The resultant force is the sum of all of the forces acting on an object.
- The change in an object’s motion is caused by the resultant force.
- If the forces acting on an object are unbalanced (not equal) it means that a resultant force is acting on the object.
Resultant force equation
- A resultant force causes an acceleration.
- The acceleration can be calculated with this equation.
- Resultant force (F) = mass (m) x acceleration (a).
- This is Newton's 2nd Law.
- Remember that the resultant force is the vector sum of all forces. You need to take into account their directions.
Test yourself on Newton's Laws
The velocity of an object will only change if it is acted on by what?
Which of the following are true?
What will happen to a moving object if there is no resultant force?
Which of these statements about acceleration are correct?
What does a resultant force cause in an object's motion?