In Investigation One, students will explore the concept of balanced forces. Students will hold objects stationary in the air and measure the force required to keep the object from accelerating. Students compare this force in Newtons to the mass of the object. Students discover that the force required to keep the object stationary is equal to the object’s weight and directly proportional to the mass of the object.

Investigation Two allows students to explore the effects of gravity in the context of unbalanced forces. Students make a small and a large object, find the mass of each object, then conduct trials to establish the time that it takes for these objects to fall to the ground. In analyzing these trials, students are introduced to the formula for calculating acceleration. Through collating and presenting their data, students come to understand that while the force of gravity is dependent on the mass of the object, acceleration due to gravity is a constant 9.8 m/s²   

During Investigation Three, students begin to investigate the force of friction. Students first learn about normal contact forces in order to provide a context for discovering friction. Students then investigate the effect of an object interacting with three different surface types. Through multiple trials, students measure the distance an object travels on these three surfaces. Students draw conclusions regarding the type of surfaces that provide the most and the least degree of frictional force.

Investigation Four introduces students to the fact that like gravity, friction can be measured using Newtons. Students understand this because they know that balanced forces cause a moving object to remain in motion and that unbalanced forces cause a moving object to accelerate. Students’ experiments lead them to realize that the frictional force constitutes an unbalanced force on a moving object. Hence, frictional force while an object is in motion causes the object to slow down. Students also discover that the frictional force acting on an object in motion is typically less than the weight of the object.

In Investigation Five, students will explore the relationship between balanced and unbalanced  force, mass, motion, and acceleration. Students first explore how forces change when a stationary object held in the air begins to move either upwards or downwards. Then, by performing an experiment in which an object is pulled horizontally, students recognize that the same principles apply. Students consider the vertical and horizontal forces acting on these stationary and moving objects and realize that the same principles apply. In doing so, students are introduced formally to Newton’s law of acceleration, which states that the sum of the forces is equal to the mass multiplied by the acceleration. 

This Performance Assessment is designed to allow students to solve a problem using the:

• concepts with which they have become familiar during the previous Investigations, and
• procedures used during the previous Investigations.