Newton’s Second Law Recall Newton’s Second Law To understand acceleration can be positive and negative Use and rearrange Newton’s 2nd Law

Which stone is harder to move and why? The heavier something is the harder it is to move it.

Acceleration means a change in velocity. If someone is accelerating at 20m/s2, they are getting faster by 20 metres per second. A car is moving at 10m/s. It starts to accelerate by 5m/s2 for three seconds. What is its final speed? Every second its speed increases by 5 seconds. It accelerates for 3 seconds, so 5+5+5= 15 15+10= 25m/s is the cars final speed.

Acceleration = change in velocity. As acceleration only means change in speed. It is possible for an object to have a negative acceleration. e.g. an acceleration of -5m/s2 would mean the object is slowing down by 5 metres per second. In everyday terms we call this decelerating. Acceleration = change in velocity. Unit = m/s2

Why? If you hit a child at 40mph there is an 80% chance they will die. If you hit a child at 30mph there is an 80% chance they will live. Why?

Mass of an average car = 1500kg. 40mph = 18m/s 30mph = 13 m/s Mass of an average car = 1500kg. When a car is in a collision it comes to a stop very quickly, so we can assume that the acceleration will be equal to the speed. Force the child is hit at = 18 x 1500 = 27,000 Newtons Force the child is hit at = 13x 1500 = 19,500 Newtons

Newton’s second law Mass = Force ÷ acceleration Acceleration = Force ÷ Mass Units: Force = Newtons (N) Acceleration = Metres per second squared (m/s2) Mass= Kilograms (Kg)

You will need

Worked Example 1 Worked Example 2 Find the force acting on an object with a mass of 10kg and an acceleration of 5m/s2. M = 10kg a = 5m/s2 F= ? F = m x a = 10 x 5 =50N 1 mark for writing the equation. 1 mark for working 1 mark for correct answer 1 mark for units. Worked Example 2 What is the acceleration of a mass of 5Kg if the resultant force is 100N? F = 100N M = 5kg a = ? F = m x a a = F ÷ m = 100 ÷ 5 = 20m/s2 1 mark for writing/rearranging the equation. 1 mark for working 1 mark for correct answer 1 mark for units. (remember if you forget the 2 you won’t get the mark!)

Practical Time 15 Minutes 15 Minutes Copy and complete this table: Height the marble is dropped from (cm) Diameter of crater (mm) 5 10 20 50 75 100 Plot your results in a line graph Remember: The scale on your graph will still need to be constant, even though you are not going up by the same amount every time.

Conclusion What did you notice? Why do you think this happened? Could you explain it in terms of Newton’s Second Law? marble dropped height bigger smaller crater acceleration deceleration force mass Model answer As the marble was dropped from a greater height the size of the crater increased. This is because the further the marble will fall the faster it will become. Meaning the bigger the deceleration of the marble when it hits the sand. According to the Newton’s second law, F=ma, the greater the acceleration the greater the force. The larger the force the larger the impact when the marble hits the sand.

Newton’s Second Law Recall Newton’s Second Law To understand acceleration can be positive and negative Use and rearrange Newton’s 2nd Law