List the names of all the forces you can think of. Questions List the names of all the forces you can think of. What do we measure force in? How do we show forces on diagrams? What forces are acting on you now? Decelerate

Explaining air resistance Air resistance is a type of friction that occurs whenever an object moves through the air. 400 N Which of these cars is more streamlined? 300 N http://www.bbc.co.uk/education/clips/z24pvcw http://www.bbc.co.uk/education/clips/zj8sb9q https://www.youtube.com/watch?v=nPSmZBmNl_k

Air resistance and drag The photo shows a streamlined car which has been shaped so that the flow of air around the body is made as smooth as possible. This minimizes the air resistance. If you looked at the car from the front, how much surface area would you see? The air resistance is determined by: the size of the car the shape of the car the speed of the car. Worksheet 2 accompanies this slide. In this worksheet, pupils must create the least streamlined car they can design. Photo credit: © 2008 Jupiterimages Corporation In your books draw and label two cars. One streamlined and one not streamlined. Explain the difference.

Balanced forces There are two wind machines applying forces to the ice skater. The forces acting on the skater are equal in magnitude and opposite in direction. The forces are balanced, so they cancel each other out. The skater does not move.

Unbalanced forces What if only one wind machine is blowing on the skater? The forces acting on her are no longer balanced so she will start to move to the left. Her speed will change – this is called acceleration. Unbalanced forces lead to a change in speed or direction.

Resultant force Teacher Notes Encourage pupils to predict the outcome of each simulation.

Balanced and unbalanced forces – summary If the forces on an object are balanced: Stationary Object: it will remain_________ Moving Object: it will ___________to move at the same ________and in a straight line. In other words, the object will continue to do what it is already doing without any change. If the forces are unbalanced, two things can happen: The speed can change. This is called______________. The ___________of motion can change.

Balanced and unbalanced forces – summary If the forces on an object are balanced: Stationary Object: it will remain stationary Moving Object: it will continue to move at the same speed and in a straight line. In other words, the object will continue to do what it is already doing without any change. If the forces are unbalanced, two things can happen: The speed can change. This is called acceleration. The direction of motion can change.